An example of text fields in Java The following applet reads text from one TextField and capitalizes it in another TextField. import java.applet.*; import java.awt.*; import java.awt.event.*; public class CapitalizeApplet extends Applet { private TextField input; private TextField output; public void init () { // Construct the TextFields this.input = new TextField(40); this.output = new TextField(40); this.output.setEditable(false); Button b = new Button("Capitalize"); // add the button to the layout this.add(input); this.add(b); this.add(output); // specify that action events sent by the // button or the input TextField should be handled // by the same CapitalizerAction object CapitalizerAction ca = new CapitalizerAction(input, output); b.addActionListener(ca); this.input.addActionListener(ca); // notice that ActionEvents produced by output are ignored. } } class CapitalizerAction implements ActionListener { private TextField in; private TextField out; public CapitalizerAction(TextField in, TextField out) { this.in = in; this.out = out; } public void actionPerformed(ActionEvent ae) { String s = in.getText(); out.setText(s.toUpperCase()); } } In this program, a different pattern is used for handling events. The constructor for the CapitalizerAction class is used to pass in references to the different components the actionPerformed() method affects. An example of text fields in Java An alternate pattern uses an inner class so the private fields can be accessed directly. import java.applet.*; import java.awt.*; import java.awt.event.*; public class CapitalizeApplet extends Applet { private TextField input; private TextField output; public void init () { // Construct the TextFields this.input = new TextField(40); this.output = new TextField(40); this.output.setEditable(false); Button b = new Button("Capitalize"); // add the button to the layout this.add(input); this.add(b); this.add(output); // specify that action events sent by the // button or the input TextField should be handled // by the same CapitalizerAction object CapitalizerAction ca = new CapitalizerAction(); b.addActionListener(ca); this.input.addActionListener(ca); // notice that ActionEvents produced by output are ignored. } class CapitalizerAction implements ActionListener { public void actionPerformed(ActionEvent ae) { String s = input.getText(); output.setText(s.toUpperCase()); } } } TextArea The java.awt.TextArea class is a subclass of java.awt.TextComponent that provides a widget for editing multiple lines of text. It's useful for input and output. There are five constructors: public TextArea() public TextArea(String text) public TextArea(int rows, int columns) public TextArea(String text, int rows, int columns) public TextArea(String text, int rows, int columns, int scrollbars) Because of the way Java lays out components, you should not use the noargs constructor. Either start off with a String or specify the number of rows and columns this area is expected to hold. For example, TextArea address = new TextArea("Type your address here", 5, 80); By default, TextAreas don't have scrollbars. However you can add them by passing one of these constants to the constructor: TextArea.SCROLLBARS_BOTH TextArea.SCROLLBARS_HORIZONTAL_ONLY TextArea.SCROLLBARS_NONE TextArea.SCROLLBARS_VERTICAL_ONLY For example, TextArea instructions = new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY); Unlike text fields, text areas do not generate action events when the user hits return inside the area. Instead, the line is broken and the caret moves on to the next row. However, the getText() method does return the contents of the TextArea, and the setText() method does change it. The setEditable() method lets you determine whether or not, the user can modify the contents of a TextField. If these methods sound familiar it's because they're both inherited from the common superclass of TextField and TextArea, TextComponent. Furthermore, you can append text to a TextArea with the append() method, insert text into the middle of a TextArea with the insert() method, and replace a block of text with the replaceRange() method: public void insert(String text, int position) public void append(String text) public void replaceRange(String text, int start, int end) TextComponent Both TextArea and TextField are subclasses of java.awt.TextComponent. This class contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable(). The TextComponent class also defines methods for manipulating the selection and the caret and for processing TextEvents. The selection is used for copy and paste and other purposes. The first character in a TextComponent is character 0; the second is character 1, and so on. public int getSelectionStart() public void setSelectionStart(int selectionStart) public int getSelectionEnd() public void setSelectionEnd(int selectionEnd) public void select(int selectionStart, int selectionEnd) public void selectAll() public String getSelectedText() The caret is the insertion point. It's where text appears when the user types. There are two methods to adjust it: public void setCaretPosition(int position) public int getCaretPosition() TextEvents Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the component changes. This is more or less every time the user hits a key in the component. The java.awt.event.TextListener interface defines a single method, textValueChanged(): public void textValueChanged(TextEvent te) You register a TextListener with a TextComponent by calling the component's addTextListener() method. For example, TextArea password = new TextArea(24) password.addTextListener(new PasswordChecker()); However, most of the time it's sufficient to just get and set the text as you need it. It's really quite rare that you need to process it character by character. A TextListener can be removed by calling removeTextListener(). public void removeTextListener(TextListener tl) java.awt.Canvas The java.awt.Canvas class is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week. The Canvas class has only three methods: public Canvas() public void addNotify() public void paint(Graphics g) You generally won't instantiate a canvas directly. Instead you'll subclass it and override the paint() method in your subclass to draw the picture you want. For example the following Canvas draws a big red oval you can add to your applet. import java.awt.*; public class RedOval extends Canvas { public void paint(Graphics g) { Dimension d = this.getSize(); g.setColor(Color.red); g.fillOval(0, 0, d.width, d.height); } public Dimension getMinimumSize() { return new Dimension(50, 100); } public Dimension getPreferredSize() { return new Dimension(150, 300); } public Dimension getMaximumSize() { return new Dimension(200, 400); } } Any applet that uses components should not also override paint(). Doing so will have unexpected effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its paint() method. Custom canvases are added to applets just like any other component. For example, public void init() { this.add(new RedOval()); } Canvases themselves do not normally fire any events. Next week, we'll see how to change that in the subclasses. An alternate approach import java.awt.*; public class ColoredOval extends Canvas { public ColoredOval() { this(Color.RED, 100, 100); } public ColoredOval(Color c) { this(c, 100, 100); } public ColoredOval(int width, int height) { this(Color.RED, width, height); } public ColoredOval(Color c, int width, int height) { this.setColor(c); this.setSize(width, height); } public void paint(Graphics g) { Dimension d = this.getSize(); g.fillOval(0, 0, d.width, d.height); } } This is almost but not quite the same effect as the previous applet. (It's a little less resizeable.) java.awt.Choice The java.awt.Choice class implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu with no fixed position. It pops up when the user clicks and holds the right mouse button.) Creating a choice menu is a little more complex than creating the other user interface components you've seen. There's an extra step, adding the menu items to the menu. That is the five steps are 1. Declare the Choice 2. Allocate the Choice 3. Add the menu items to the Choice 4. Add the Choice to the layout 5. Add an ItemListener to the Choice For example public void init() { Choice ch; ch = new Choice(); ch.addItem("1"); ch.addItem("2"); ch.addItem("3"); ch.addItem("4"); ch.addItem("5"); add(ch); } Methods of java.awt.Choice The Choice class has a number of methods to add, remove, and return different items from the list. The list starts counting at 0. public int getItemCount() public String getItem(int index) public void add(String item) public void addItem(String item) public void insert(String item, int position) public void remove(String item) public void remove(int position) public void removeAll() However, most of the item you'll just build the Choice when the applet starts up, and not modify it later. These methods get or set the current selected item in the Choice, that is the item that's shown. public void removeAll() public String getSelectedItem() public Object[] getSelectedObjects() public int getSelectedIndex() public void select(int position) public void select(String item) ItemListeners When the user changes the selected item in a Choice, the Choice fires two ItemListener events, one to indicate that the original selection has been deselected and the other to indicate that a new selection has been made. You can process these events by registering an ItemListener object with your Choice. You do not always need to do this. It is not uncommon to only check the value of a Choice when some other event occurs like a Button press. For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user makes a selection, the applet beeps that many times. import java.applet.*; import java.awt.*; import java.awt.event.*; public class MultiBeep extends Applet { public void init() { Choice ch; ch = new Choice(); ch.addItem("1"); ch.addItem("2"); ch.addItem("3"); ch.addItem("4"); ch.addItem("5"); this.add(ch); ch.addItemListener(new BeepItem()); } } class BeepItem implements ItemListener { public void itemStateChanged(ItemEvent ie) { if (ie.getStateChange() == ItemEvent.SELECTED) { String name = (String) ie.getItem(); Toolkit tk = Toolkit.getDefaultToolkit(); try { int n = Integer.parseInt(name); for (int i = 0; i < n; i++) tk.beep(); } catch (Exception e) { tk.beep(); } } } } The BeepItem class implements the ItemListener interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only beeps if an item was selected. The available convenience constants you can check are: ItemEvent.DESELECTED ItemEvent.ITEM_FIRST ItemEvent.ITEM_LAST ItemEvent.ITEM_STATE_CHANGED ItemEvent.SELECTED The ItemEvent.getItem() method is used to retrieve the actual selected item. java.awt.Checkbox Check boxes are used to select a boolean value. Each Checkbox has a label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label "Anchovies" would be checked if the user wants anchovies on their pizza and unchecked if they don't. Checkboxes are often used to select from a list of possible choices when as few selections as zero or as many as everything on the list may be made. Adding a Checkbox to an applet is simple. Just declare it, construct it and add it. Checkbox c c = new Checkbox("Pepperoni")); add(c); As usual these steps may be combined into the single line add(new Checkbox("Pepperoni")); By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the following constructor instead: add(new Checkbox("Pepperoni", null, true)); The null is a reference to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup. Every Checkbox has a boolean value, either true or false. When the Checkbox is checked that value is true. When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean b) methods. For example private void handleCheckbox(Checkbox c) { if (c.getState()) price += 0.50; else price -= 0.50; } Checkbox Events When the a Checkbox changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore this event. Instead you manually check the state of a Checkbox when you need to know it. However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. An ItemEvent is exactly the same as the item event fired by a Choice. In fact item events are used to indicate selections or deselections in any sort of list including checkboxes, radio buttons, choices, and lists. For example, the following program is an applet that asks the age-old question, "What do you want on your pizza?" When an ingredient is checked the price of the pizza goes up by fifty cents. When an ingredient is unchecked fifty cents is taken off. The price is shown in a TextField. import java.applet.*; import java.awt.*; import java.awt.event.*; public class Ingredients extends Applet { private TextField display; private double price = 7.00; public void init() { this.add(new Label("What do you want on your pizza?", Label.CENTER)); Pricer p = new Pricer(this); Checkbox pepperoni = new Checkbox("Pepperoni"); this.add(pepperoni); pepperoni.addItemListener(p); Checkbox olives = new Checkbox("Olives"); olives.addItemListener(p); this.add(olives); Checkbox onions = new Checkbox("Onions"); onions.addItemListener(p); this.add(onions); Checkbox sausage = new Checkbox("Sausage"); sausage.addItemListener(p); this.add(sausage); Checkbox peppers = new Checkbox("Peppers"); peppers.addItemListener(p); this.add(peppers); Checkbox extraCheese = new Checkbox("Extra Cheese"); extraCheese.addItemListener(p); this.add(extraCheese); Checkbox ham = new Checkbox("Ham"); ham.addItemListener(p); this.add(ham); Checkbox pineapple = new Checkbox("Pineapple"); pineapple.addItemListener(p); this.add(pineapplec); Checkbox anchovies = new Checkbox("Anchovies"); anchovies.addItemListener(p); this.add(anchovies); this.display = new TextField(String.valueOf(price)); // so people can't change the price of the pizza display.setEditable(false); this.add(display); } public void setPrice(double price) { this.price = price; display.setText(String.valueOf(price)); } public double getPrice() { return this.price; } } class Pricer implements ItemListener { private Ingredients out; public Pricer(Ingredients out) { this.out = out; } public void itemStateChanged(ItemEvent ie) { double price = out.getPrice(); if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50; else price -= 0.50; // Change the price out.setPrice(price); } } java.awt.CheckboxGroup Checkbox groups are collections of checkboxes with the special property that no more than one checkbox in the same group can be selected at a time. The checkboxes in a CheckboxGroup are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked simultaneously. When the user checks one, all others are unchecked automatically. The constructor for a CheckboxGroup is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since checkbox groups are themselves not user-interface widgets, just ways of arranging checkboxes. CheckboxGroup cbg = new CheckboxGroup(); To make check boxes act like radio buttons, use this constructor for each Checkbox in the group. public Checkbox(String label, CheckboxGroup cbg, boolean checked) The label is the label for this Checkbox. The CheckboxGroup is the group you want this Checkbox to belong to and must already exist. At any time, you can get or set the selected Checkbox with these two methods: public Checkbox getSelectedCheckbox() public void setSelectedCheckbox(Checkbox box) java.awt.CheckboxGroup example The following program asks the customer how they're going to pay for their pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may want both anchovies and pineapple on their pizza, but they're unlikely to pay with both Visa and American Express. import java.applet.*; import java.awt.*; public class PaymentMethod extends Applet { public void init() { this.add(new Label("How will you pay for your pizza?")); CheckboxGroup cbg = new CheckboxGroup(); this.add(new Checkbox("Visa", cbg, false)); this.add(new Checkbox("Mastercard", cbg, false)); this.add(new Checkbox("American Express", cbg, false)); this.add(new Checkbox("Discover", cbg, false)); this.add(new Checkbox("Cash", cbg, true)); // the default } } There isn't any action in this simple example applet. If you need to add action as radio buttons are checked and unchecked, you do it just the same as for any other Checkbox. java.awt.List Scrolling lists are useful for storing long lists of things one to a line. The things in the list are called items, but each one is just a String. For example, List Methods You create a new List with one of these three constructors: public List() public List(int numLines) public List(int numLines, boolean allowMultipleSelections) For example, List l = new List(8, true); numLines is the number of items you want to be visible in the scrolling list. It is not necessarily the same as the number of items in the list which is limited only by available memory. allowMultipleSelections says whether the user is allowed to select more than one item at once (typically by Shift-clicking). The following methods add items at the end of the list: public void add(String item) public void addItem(String item) These two methods add items at the specified position in the list. public void add(String item, int index) public void addItem(String item, int index) The following methods remove items from the List: public void removeAll() public void remove(String item) public void remove(int position) public void delItem(int position) These methods allow you to retrive particular items from the List: public int getItemCount() public String getItem(int index) public String[] getItems() You ran also replace a particular item: public void replaceItem(String newValue, int index) These methods allow you to determine which item the user has selected: public int getSelectedIndex() public int[] getSelectedIndexes() public String getSelectedItem() public String[] getSelectedItems() public Object[] getSelectedObjects() If a list allows multiple selections, you should use the plural forms of the above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). public boolean isMultipleMode() public void setMultipleMode(boolean b) These methods allow you to manipulate the selection: public void select(int index) public void deselect(int index) public boolean isIndexSelected(int index) These two methods determine whether an item at a particular index is currently visible in the List box: public int getVisibleIndex() public void makeVisible(int index) List Events Lists can fire two separate types of events. When a list item is selected or deselected, the List fires an ItemEvent. However, when the user double clicks on a list item, the List fires an ActionEvent. Therefore, you can register both an ItemListener to process selections and/or an ActionListener to process double clicks. public void addItemListener(ItemListener l) public void removeItemListener(ItemListener l) public void addActionListener(ActionListener l) public void removeActionListener(ActionListener l) The action command in the ActionEvent is the list item which was double clicked. java.awt.Scrollbar Lists, TextAreas, and ScrollPanes come with ready made scrollbars. However if you want to scroll any other object you'll have to use a java.awt.Scrollbar. Scrollbars have many uses. At their most basic they're used for moving the visible area. They can also be used to set a value between two numbers. Or they can be used to flip through a number of screens as in a database operation that looks at successive records. There are three constructors: public Scrollbar() public Scrollbar(int orientation) public Scrollbar(int orientation, int value, int visible, int min, int max) The orientation argument is one of the mnemonic constants, Scrollbar.HORIZONTAL or Scrollbar.VERTICAL. As you expect this determines whether the Scrollbar is laid out from left to right or top to bottom. A Scrollbar has an int value at all times. This value will be between the minimum and the maximum value set by the last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0. Finally visible represents the size of the visible portion of the scrollable area in pixels. The Scrollbar uses this when moving up or down a page. A Scrollbar fires an adjustment event when its value changes. You register an adjustment listener to catch this event. This class needs an adjustmentValueChanged() method with this signature: public void adjustmentValueChanged(AdjustmentEvent e) The following program is an applet that changes the number in a TextField between 1 and 100 based on the position of the thumb (the movable part of the Scrollbar). In a practical application the number would of course mean something. import java.applet.*; import java.awt.*; import java.awt.event.*; public class Scrollie extends Applet implements AdjustmentListener { private TextField t; private Scrollbar sb; public void init() { int initialValue = 1; sb = new Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100); sb.addAdjustmentListener(this); this.add(sb); this.t = new TextField(4); this.t.setText(String.valueOf(initialValue)); this.add(t); } public void adjustmentValueChanged(AdjustmentEvent e) int val = sb.getValue(); this.t.setText(String.valueOf(val)); } } Peer vs. Swing Components I'm not going to talk much about Swing in this course, but most of what I teach you about the standard AWT components carries over to their Swing equivalents with only trivial changes. For example, here's yet another way to write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold and blue and with a yellow background. import java.awt.*; import javax.swing.*; public class SwingCubScout extends JApplet { public void init() { JLabel cubScouts = new JLabel("Cub Scouts!"); cubScouts.setForeground(Color.blue); cubScouts.setBackground(Color.yellow); cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); this.getContentPane().add(cubScouts); } } This is almost identical to the AWT-based Cub Scout applet, except that I've imported the javax.swing package and changed Label to JLabel and Applet to JApplet. Week 6 Exercises 1. Write an applet that with a 60 column by 10 row text area that allows the user to type some text. Add a button to this applet that clears the text area when it's pressed. Don't worry excessively about making the applet look good. Before you can do that you'll need to learn about layout managers. 2. Rewrite the payroll problem from week 2 as an applet. Provide a text field for the number of hours, a text field for the pay rate, and a non-editable text field for the output. Also provide labels to identify all three text fields and a button to calculate the result. Don't worry about minimum wage, number of hours in the week, or other error conditions we checked before. In the event the user enters data that cannot be interpreted as a number, don't put anything in the output text field. In a couple of weeks, you'll learn how to bring up an error dialog to handle these conditions. Don't worry excessively about making the applet look good. Before you can do that you'll need to learn about layout managers. We'll cover them next week Getting into more fun Graphics import java.awt.*; import java.awt.event.*; import javax.swing.*; public class ShowColors2 extends JFrame { private JButton changeColorButton; private Color color = Color.LIGHT_GRAY; private Container container; // set up GUI public ShowColors2() { super( "Using JColorChooser" ); container = getContentPane(); container.setLayout( new FlowLayout() ); // set up changeColorButton and register its event handler changeColorButton = new JButton( "Change Color" ); changeColorButton.addActionListener( new ActionListener() { // anonymous inner class // display JColorChooser when user clicks button public void actionPerformed( ActionEvent event ) { color = JColorChooser.showDialog( ShowColors2.this, "Choose a color", color ); // set default color, if no color is returned if ( color == null ) color = Color.LIGHT_GRAY; // change content pane's background color container.setBackground( color ); } } // end anonymous inner class ); // end call to addActionListener container.add( changeColorButton ); setSize( 400, 130 ); setVisible( true ); } // end ShowColor2 constructor // execute application public static void main( String args[] ) { ShowColors2 application = new ShowColors2(); application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); } } import java.awt.*; import java.awt.geom.*; import javax.swing.*; public class Shapes2 extends JFrame { // set window's title bar String, background color and dimensions public Shapes2() { super( "Drawing 2D Shapes" ); getContentPane().setBackground( Color.WHITE ); setSize( 400, 400 ); setVisible( true ); } // draw general paths public void paint( Graphics g ) { super.paint( g ); // call superclass's paint method int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 }; int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 }; Graphics2D g2d = ( Graphics2D ) g; GeneralPath star = new GeneralPath(); // create GeneralPath object // set the initial coordinate of the General Path star.moveTo( xPoints[ 0 ], yPoints[ 0 ] ); // create the star--this does not draw the star for ( int count = 1; count < xPoints.length; count++ ) star.lineTo( xPoints[ count ], yPoints[ count ] ); star.closePath(); // close the shape g2d.translate( 200, 200 ); // translate the origin to (200, 200) // rotate around origin and draw stars in random colors for ( int count = 1; count <= 20; count++ ) { g2d.rotate( Math.PI / 10.0 ); // rotate coordinate system // set random drawing color g2d.setColor( new Color( ( int ) ( Math.random() * 256 ), ( int ) ( Math.random() * 256 ), ( int ) ( Math.random() * 256 ) ) ); g2d.fill( star ); // draw filled star } } // end method paint // execute application public static void main( String args[] ) { Shapes2 application = new Shapes2(); application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); } }

An example of text fields in Java

The following applet reads text from one TextField and capitalizes it in another TextField.

import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class CapitalizeApplet extends Applet {

  private TextField input;

  private TextField output;

  public void init () {

     // Construct the TextFields

     this.input = new TextField(40);

     this.output = new TextField(40);

     this.output.setEditable(false);

     Button b = new Button("Capitalize");

     // add the button to the layout

     this.add(input);

     this.add(b);

     this.add(output);

     // specify that action events sent by the

     // button or the input TextField should be handled 

     // by the same CapitalizerAction object

     CapitalizerAction ca = new CapitalizerAction(input, output);

     b.addActionListener(ca);

     this.input.addActionListener(ca);

     // notice that ActionEvents produced by output are ignored.

   }

}

class CapitalizerAction implements ActionListener {

  private TextField in;

  private TextField out;

  public CapitalizerAction(TextField in, TextField out) {

    this.in = in;

    this.out = out;

  }

  public void actionPerformed(ActionEvent ae) {

    String s = in.getText();

    out.setText(s.toUpperCase());

  }

}

In this program, a different pattern is used for handling events. The constructor for the CapitalizerAction class is used to pass in references to the different components the actionPerformed() method affects.

An example of text fields in Java

An alternate pattern uses an inner class so the private fields can be accessed directly.

import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class CapitalizeApplet extends Applet {

  private TextField input;

  private TextField output;

  public void init () {

     // Construct the TextFields

     this.input = new TextField(40);

     this.output = new TextField(40);

     this.output.setEditable(false);

     Button b = new Button("Capitalize");

     // add the button to the layout

     this.add(input);

     this.add(b);

     this.add(output);

     // specify that action events sent by the

     // button or the input TextField should be handled 

     // by the same CapitalizerAction object

     CapitalizerAction ca = new CapitalizerAction();

     b.addActionListener(ca);

     this.input.addActionListener(ca);

     // notice that ActionEvents produced by output are ignored.

   }

  class CapitalizerAction implements ActionListener {

    public void actionPerformed(ActionEvent ae) {

      String s = input.getText();

      output.setText(s.toUpperCase());

    }

  }

}

TextArea

The java.awt.TextArea class is a subclass of java.awt.TextComponent that provides a widget for editing multiple lines of text. It's useful for input and output.

There are five constructors:

  public TextArea()

  public TextArea(String text)

  public TextArea(int rows, int columns)

  public TextArea(String text, int rows, int columns)

  public TextArea(String text, int rows, int columns, int scrollbars)

Because of the way Java lays out components, you should not use the noargs constructor. Either start off with a String or specify the number of rows and columns this area is expected to hold. For example,

TextArea address = new TextArea("Type your address here", 5, 80);

By default, TextAreas don't have scrollbars. However you can add them by passing one of these constants to the constructor:

TextArea.SCROLLBARS_BOTH 

TextArea.SCROLLBARS_HORIZONTAL_ONLY 

TextArea.SCROLLBARS_NONE 

TextArea.SCROLLBARS_VERTICAL_ONLY

For example,

TextArea instructions = 

 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);

Unlike text fields, text areas do not generate action events when the user hits return inside the area. Instead, the line is broken and the caret moves on to the next row.
However, the getText() method does return the contents of the TextArea, and the setText() method does change it. The setEditable() method lets you determine whether or not, the user can modify the contents of a TextField. If these methods sound familiar it's because they're both inherited from the common superclass of TextField and TextArea, TextComponent.
Furthermore, you can append text to a TextArea with the append() method, insert text into the middle of a TextArea with the insert() method, and replace a block of text with the replaceRange() method:

public void insert(String text, int position)

public void append(String text)  

public void replaceRange(String text, int start, int end)

TextComponent

Both TextArea and TextField are subclasses of java.awt.TextComponent. This class contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable(). The TextComponent class also defines methods for manipulating the selection and the caret and for processing TextEvents.
The selection is used for copy and paste and other purposes. The first character in a TextComponent is character 0; the second is character 1, and so on.

  public int    getSelectionStart()

  public void   setSelectionStart(int selectionStart)

  public int    getSelectionEnd()

  public void   setSelectionEnd(int selectionEnd)

  public void   select(int selectionStart, int selectionEnd)

  public void   selectAll()

  public String getSelectedText()

The caret is the insertion point. It's where text appears when the user types. There are two methods to adjust it:

  public void setCaretPosition(int position)

  public int  getCaretPosition()

TextEvents

Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the component changes. This is more or less every time the user hits a key in the component.
The java.awt.event.TextListener interface defines a single method, textValueChanged():

public void textValueChanged(TextEvent te)

You register a TextListener with a TextComponent by calling the component's addTextListener() method. For example,

TextArea password = new TextArea(24)

password.addTextListener(new PasswordChecker());

However, most of the time it's sufficient to just get and set the text as you need it. It's really quite rare that you need to process it character by character.
A TextListener can be removed by calling removeTextListener().
public void removeTextListener(TextListener tl)

java.awt.Canvas

The java.awt.Canvas class is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week. The Canvas class has only three methods:

  public Canvas()

  public void addNotify()

  public void paint(Graphics g)

You generally won't instantiate a canvas directly. Instead you'll subclass it and override the paint() method in your subclass to draw the picture you want.
For example the following Canvas draws a big red oval you can add to your applet.

import java.awt.*;

public class RedOval extends Canvas {

  public void paint(Graphics g) {

    Dimension d = this.getSize();

    g.setColor(Color.red);

    g.fillOval(0, 0, d.width, d.height);

  }

  public Dimension getMinimumSize() {

    return new Dimension(50, 100);  

  }

  public Dimension getPreferredSize() {

    return new Dimension(150, 300);  

  }

  public Dimension getMaximumSize() {

    return new Dimension(200, 400);  

  }

}

Any applet that uses components should not also override paint(). Doing so will have unexpected effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its paint() method.
Custom canvases are added to applets just like any other component. For example,

  public void init() {

    this.add(new RedOval());

  }

Canvases themselves do not normally fire any events. Next week, we'll see how to change that in the subclasses.

An alternate approach

import java.awt.*;

public class ColoredOval extends Canvas {

  public ColoredOval() {

    this(Color.RED, 100, 100);

  }

  public ColoredOval(Color c) {

    this(c, 100, 100);

  }

  public ColoredOval(int width, int height) {

    this(Color.RED, width, height);

  }

  public ColoredOval(Color c, int width, int height) {

    this.setColor(c);

    this.setSize(width, height);

  }

  public void paint(Graphics g) {  

    Dimension d = this.getSize();

    g.fillOval(0, 0, d.width, d.height);

  }

}

This is almost but not quite the same effect as the previous applet. (It's a little less resizeable.)

java.awt.Choice

The java.awt.Choice class implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu with no fixed position. It pops up when the user clicks

and holds the right mouse button.)

Creating a choice menu is a little more complex than creating the other user interface components you've seen. There's an extra step, adding the menu items to the menu. That is the five steps are

1. Declare the Choice
2. Allocate the Choice
3. Add the menu items to the Choice
4. Add the Choice to the layout
5. Add an ItemListener to the Choice

For example

 public void init() {

    Choice ch;

    ch = new Choice();

    ch.addItem("1");

    ch.addItem("2");

    ch.addItem("3");

    ch.addItem("4");

    ch.addItem("5");

    add(ch);

  }   

Methods of java.awt.Choice

The Choice class has a number of methods to add, remove, and return different items from the list. The list starts counting at 0.

  public int    getItemCount()

  public String getItem(int index)

  public void   add(String item)

  public void   addItem(String item)

  public void   insert(String item, int position)

  public void   remove(String item)

  public void   remove(int position)

  public void   removeAll()

However, most of the item you'll just build the Choice when the applet starts up, and not modify it later.
These methods get or set the current selected item in the Choice, that is the item that's shown.

  public void     removeAll()

  public String   getSelectedItem()

  public Object[] getSelectedObjects()

  public int      getSelectedIndex()

  public void     select(int position)

  public void     select(String item)

ItemListeners

When the user changes the selected item in a Choice, the Choice fires two ItemListener events, one to indicate that the original selection has been deselected and the other to indicate that a new selection has been made. You can process these events by registering an ItemListener object with your Choice.
You do not always need to do this. It is not uncommon to only check the value of a Choice when some other event occurs like a Button press.
For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user makes a selection, the applet beeps that many times.

import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class MultiBeep extends Applet {

  public void init() {

    Choice ch;

    ch = new Choice();

    ch.addItem("1");

    ch.addItem("2");

    ch.addItem("3");

    ch.addItem("4");

    ch.addItem("5");

    this.add(ch);

    ch.addItemListener(new BeepItem());

  }    

}

class BeepItem implements ItemListener {

  public void itemStateChanged(ItemEvent ie) {

    if (ie.getStateChange() == ItemEvent.SELECTED) {

      String name = (String) ie.getItem();

      Toolkit tk = Toolkit.getDefaultToolkit();

      try {

        int n = Integer.parseInt(name);

        for (int i = 0; i < n; i++) tk.beep();

      }

      catch (Exception e) {

        tk.beep();

      }

    }

  }

}

The BeepItem class implements the ItemListener interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only beeps if an item was selected. The available convenience constants you can check are:

ItemEvent.DESELECTED 

ItemEvent.ITEM_FIRST 

ItemEvent.ITEM_LAST 

ItemEvent.ITEM_STATE_CHANGED 

ItemEvent.SELECTED

The ItemEvent.getItem() method is used to retrieve the actual selected item.

java.awt.Checkbox

Check boxes are used to select a boolean value. Each Checkbox has a label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label "Anchovies" would be checked if the user wants anchovies on their pizza and unchecked if they don't.

Checkboxes are often used to select from a list of possible choices when as few selections as zero or as many as everything on the list may be made. Adding a Checkbox to an applet is simple. Just declare it, construct it and add it.

  Checkbox c c = new Checkbox("Pepperoni"));

  add(c);

As usual these steps may be combined into the single line
add(new Checkbox("Pepperoni"));
By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the following constructor instead:
add(new Checkbox("Pepperoni", null, true));
The null is a reference to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.
Every Checkbox has a boolean value, either true or false. When the Checkbox is checked that value is true. When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean b) methods. For example

  private void handleCheckbox(Checkbox c) {

    if (c.getState()) price += 0.50;

    else price -= 0.50;

  }

Checkbox Events

When the a Checkbox changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore this event. Instead you manually check the state of a Checkbox when you need to know it. However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox.
An ItemEvent is exactly the same as the item event fired by a Choice. In fact item events are used to indicate selections or deselections in any sort of list including checkboxes, radio buttons, choices, and lists.
For example, the following program is an applet that asks the age-old question, "What do you want on your pizza?" When an ingredient is checked the price of the pizza goes up by fifty cents. When an ingredient is unchecked fifty cents is taken off. The price is shown in a TextField.

import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class Ingredients extends Applet {

  private TextField display;

  private double price = 7.00;

  public void init() {

    this.add(new Label("What do you want on your pizza?", Label.CENTER));

    Pricer p = new Pricer(this);

    Checkbox pepperoni = new Checkbox("Pepperoni");

    this.add(pepperoni);

    pepperoni.addItemListener(p);

    Checkbox olives = new Checkbox("Olives");

    olives.addItemListener(p);

    this.add(olives);

    Checkbox onions = new Checkbox("Onions");

    onions.addItemListener(p);

    this.add(onions);

    Checkbox sausage = new Checkbox("Sausage");

    sausage.addItemListener(p);

    this.add(sausage);

    Checkbox peppers = new Checkbox("Peppers");

    peppers.addItemListener(p);

    this.add(peppers);

    Checkbox extraCheese = new Checkbox("Extra Cheese");

    extraCheese.addItemListener(p);

    this.add(extraCheese);

    Checkbox ham = new Checkbox("Ham");

    ham.addItemListener(p);

    this.add(ham);

    Checkbox pineapple = new Checkbox("Pineapple");

    pineapple.addItemListener(p);

    this.add(pineapplec);

    Checkbox anchovies = new Checkbox("Anchovies");

    anchovies.addItemListener(p);

    this.add(anchovies);

    this.display = new TextField(String.valueOf(price));

    // so people can't change the price of the pizza

    display.setEditable(false); 

    this.add(display);

  }

  public void setPrice(double price) {

    this.price = price;

    display.setText(String.valueOf(price));

  }

  public double getPrice() {

    return this.price;

  }

}

class Pricer implements ItemListener {

  private Ingredients out;

  public Pricer(Ingredients out) {

    this.out = out;

  }

  public void itemStateChanged(ItemEvent ie) {

    double price = out.getPrice();

    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;

    else price -= 0.50;

    // Change the price

    out.setPrice(price);

  }

}

java.awt.CheckboxGroup

Checkbox groups are collections of checkboxes with the special property that no more than one checkbox in the same group can be selected at a time. The checkboxes in a CheckboxGroup are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked simultaneously. When the user checks one, all others are unchecked automatically.
The constructor for a CheckboxGroup is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since checkbox groups are themselves not user-interface widgets, just ways of arranging checkboxes.
CheckboxGroup cbg = new CheckboxGroup();
To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.
public Checkbox(String label, CheckboxGroup cbg, boolean checked)
The label is the label for this Checkbox. The CheckboxGroup is the group you want this Checkbox to belong to and must already exist.
At any time, you can get or set the selected Checkbox with these two methods:

  public Checkbox getSelectedCheckbox()

  public void setSelectedCheckbox(Checkbox box)

java.awt.CheckboxGroup example

The following program asks the customer how they're going to pay for their pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may want both anchovies and pineapple on their pizza, but they're unlikely to pay with both Visa and American Express.

import java.applet.*;    

import java.awt.*;

public class PaymentMethod extends Applet {

  public void init() {

    this.add(new Label("How will you pay for your pizza?"));

    CheckboxGroup cbg = new CheckboxGroup();

    this.add(new Checkbox("Visa", cbg, false));

    this.add(new Checkbox("Mastercard", cbg, false));

    this.add(new Checkbox("American Express", cbg, false));

    this.add(new Checkbox("Discover", cbg, false));

    this.add(new Checkbox("Cash", cbg, true)); // the default

  }

}

There isn't any action in this simple example applet. If you need to add action as radio buttons are checked and unchecked, you do it just the same as for any other Checkbox.

java.awt.List

Scrolling lists are useful for storing long lists of things one to a line. The things in the list are called items, but each one is just a String. For example,

List Methods

You create a new List with one of these three constructors:

  public List()

  public List(int numLines)

  public List(int numLines, boolean allowMultipleSelections)

For example,
List l = new List(8, true);
numLines is the number of items you want to be visible in the scrolling list. It is not necessarily the same as the number of items in the list which is limited only by available memory. allowMultipleSelections says whether the user is allowed to select more than one item at once (typically by Shift-clicking).
The following methods add items at the end of the list:

  public void add(String item)

  public void addItem(String item)

These two methods add items at the specified position in the list.

  public void add(String item, int index)

  public void addItem(String item, int index)

The following methods remove items from the List:

  public void removeAll()

  public void remove(String item)

  public void remove(int position)

  public void delItem(int position)

These methods allow you to retrive particular items from the List:

  public int getItemCount()

  public String getItem(int index)

  public String[] getItems()

You ran also replace a particular item:

 public void replaceItem(String newValue, int index)

These methods allow you to determine which item the user has selected:

  public int      getSelectedIndex()

  public int[]    getSelectedIndexes()

  public String   getSelectedItem()

  public String[] getSelectedItems()

  public Object[] getSelectedObjects()

If a list allows multiple selections, you should use the plural forms of the above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode().

  public boolean isMultipleMode()

  public void    setMultipleMode(boolean b)

These methods allow you to manipulate the selection:

  public void    select(int index)

  public void    deselect(int index)

  public boolean isIndexSelected(int index)

These two methods determine whether an item at a particular index is currently visible in the List box:

  public int  getVisibleIndex()

  public void makeVisible(int index)

List Events

Lists can fire two separate types of events. When a list item is selected or deselected, the List fires an ItemEvent. However, when the user double clicks on a list item, the List fires an ActionEvent. Therefore, you can register both an ItemListener to process selections and/or an ActionListener to process double clicks.

public void addItemListener(ItemListener l)

public void removeItemListener(ItemListener l)

public void addActionListener(ActionListener l)

public void removeActionListener(ActionListener l)

The action command in the ActionEvent is the list item which was double clicked.

java.awt.Scrollbar

Lists, TextAreas, and ScrollPanes come with ready made scrollbars. However if you want to scroll any other object you'll have to use a java.awt.Scrollbar. Scrollbars have many uses. At their most basic they're used for moving the visible area. They can also be used to set a value between two numbers. Or they can be used to flip through a number of screens as in a database operation that looks at successive records.
There are three constructors:

public Scrollbar()

public Scrollbar(int orientation)

public Scrollbar(int orientation, int value, int visible, int min, int max)

The orientation argument is one of the mnemonic constants, Scrollbar.HORIZONTAL or Scrollbar.VERTICAL. As you expect this determines whether the Scrollbar is laid out from left to right or top to bottom.
A Scrollbar has an int value at all times. This value will be between the minimum and the maximum value set by the last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.
Finally visible represents the size of the visible portion of the scrollable area in pixels. The Scrollbar uses this when moving up or down a page.
A Scrollbar fires an adjustment event when its value changes. You register an adjustment listener to catch this event. This class needs an adjustmentValueChanged() method with this signature:
public void adjustmentValueChanged(AdjustmentEvent e)
The following program is an applet that changes the number in a TextField between 1 and 100 based on the position of the thumb (the movable part of the Scrollbar). In a practical application the number would of course mean something.

import java.applet.*;    

import java.awt.*;

import java.awt.event.*;

public class Scrollie extends Applet implements AdjustmentListener {

  private TextField t;

  private Scrollbar sb;

  public void init() {

    int initialValue = 1;

    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);

    sb.addAdjustmentListener(this);

    this.add(sb);

    this.t = new TextField(4);

    this.t.setText(String.valueOf(initialValue));    

    this.add(t);

  }

  public void adjustmentValueChanged(AdjustmentEvent e)

    int val = sb.getValue();

    this.t.setText(String.valueOf(val));

  }

}

Peer vs. Swing Components

I'm not going to talk much about Swing in this course, but most of what I teach you about the standard AWT components carries over to their Swing equivalents with only trivial changes. For example, here's yet another way to write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold and blue and with a yellow background.

import java.awt.*;

import javax.swing.*;

public class SwingCubScout extends JApplet {

  public void init() {

     JLabel cubScouts = new JLabel("Cub Scouts!");

     cubScouts.setForeground(Color.blue);

     cubScouts.setBackground(Color.yellow);

     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 

     this.getContentPane().add(cubScouts);

  }

}

This is almost identical to the AWT-based Cub Scout applet, except that I've imported the javax.swing package and changed Label to JLabel and Applet to JApplet.

Week 6 Exercises

1. Write an applet that with a 60 column by 10 row text area that allows the user to type some text. Add a button to this applet that clears the text area when it's pressed.

Don't worry excessively about making the applet look good. Before you can do that you'll need to learn about layout managers.

2. Rewrite the payroll problem from week 2 as an applet. Provide a text field for the number of hours, a text field for the pay rate, and a non-editable text field for the output. Also provide labels to identify all three text fields and a button to calculate the result.

Don't worry about minimum wage, number of hours in the week, or other error conditions we checked before. In the event the user enters data that cannot be interpreted as a number, don't put anything in the output text field. In a couple of weeks, you'll learn how to bring up an error dialog to handle these conditions.

Don't worry excessively about making the applet look good. Before you can do that you'll need to learn about layout managers. We'll cover them next week

Getting into more fun Graphics

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class ShowColors2 extends JFrame {

   private JButton changeColorButton;

   private Color color = Color.LIGHT_GRAY;

   private Container container;

   // set up GUI

   public ShowColors2()

   {

      super( "Using JColorChooser" );

      container = getContentPane();

      container.setLayout( new FlowLayout() );

      // set up changeColorButton and register its event handler

      changeColorButton = new JButton( "Change Color" );

      changeColorButton.addActionListener(

         new ActionListener() {  // anonymous inner class

            // display JColorChooser when user clicks button

            public void actionPerformed( ActionEvent event )

            {

               color = JColorChooser.showDialog( 

                  ShowColors2.this, "Choose a color", color );

               // set default color, if no color is returned 

               if ( color == null )

                  color = Color.LIGHT_GRAY;

               // change content pane's background color

               container.setBackground( color );

            }

         } // end anonymous inner class

      ); // end call to addActionListener

      container.add( changeColorButton );

      setSize( 400, 130 );

      setVisible( true );

   } // end ShowColor2 constructor

   // execute application

   public static void main( String args[] )

   {

      ShowColors2 application = new ShowColors2();

      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

   }

}

import java.awt.*;

import java.awt.geom.*;

import javax.swing.*;

public class Shapes2 extends JFrame {

   // set window's title bar String, background color and dimensions

   public Shapes2()

   {

      super( "Drawing 2D Shapes" );

      getContentPane().setBackground( Color.WHITE );

      setSize( 400, 400 );

      setVisible( true );

   }

   // draw general paths

   public void paint( Graphics g )

   {

      super.paint( g );  // call superclass's paint method

      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };

      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };

      Graphics2D g2d = ( Graphics2D ) g;

      GeneralPath star = new GeneralPath();  // create GeneralPath object

      // set the initial coordinate of the General Path

      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );

      // create the star--this does not draw the star

      for ( int count = 1; count < xPoints.length; count++ )

         star.lineTo( xPoints[ count ], yPoints[ count ] );

      star.closePath();  // close the shape

      g2d.translate( 200, 200 );  // translate the origin to (200, 200)

      // rotate around origin and draw stars in random colors

      for ( int count = 1; count <= 20; count++ ) {

         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system

         // set random drawing color

         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),

            ( int ) ( Math.random() * 256 ),              

            ( int ) ( Math.random() * 256 ) ) );

         g2d.fill( star );  // draw filled star

      }

   } // end method paint

   // execute application

   public static void main( String args[] )

   {

      Shapes2 application = new Shapes2();

      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

   }

} 

An example of text fields in Java
The following applet reads text from one TextField
and capitalizes it in another TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction(input, output);
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
}
 
 
class CapitalizerAction implements ActionListener {
 
  private TextField in;
  private TextField out;
 
  public CapitalizerAction(TextField in, TextField out) {
    this.in = in;
    this.out = out;
  }
 
  public void actionPerformed(ActionEvent ae) {
 
    String s = in.getText();
    out.setText(s.toUpperCase());
 
  }
 
}
In this program, a different pattern is used for handling events. The
constructor for the CapitalizerAction
class is used to pass in references to the different components the actionPerformed() method affects. 




An example of text fields in Java
An alternate pattern uses an inner class so the private fields can be
accessed directly.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction();
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
  class CapitalizerAction implements ActionListener {
 
    public void actionPerformed(ActionEvent ae) {
 
      String s = input.getText();
      output.setText(s.toUpperCase());
 
    }
 
  }
 
 
}

TextArea
The java.awt.TextArea
class is a subclass of java.awt.TextComponent
that provides a widget for editing multiple lines of text. It's useful for
input and output.







There are five constructors:



  public TextArea()
  public TextArea(String text)
  public TextArea(int rows, int columns)
  public TextArea(String text, int rows, int columns)
  public TextArea(String text, int rows, int columns, int scrollbars)
Because of the way Java lays out components, you should not use the noargs
constructor. Either start off with a String
or specify the number of rows and columns this area is expected to hold. For
example, 



TextArea address = new TextArea("Type your address here", 5, 80);
By default, TextAreas don't have scrollbars. However you can add them by
passing one of these constants to the constructor: 



TextArea.SCROLLBARS_BOTH 
TextArea.SCROLLBARS_HORIZONTAL_ONLY 
TextArea.SCROLLBARS_NONE 
TextArea.SCROLLBARS_VERTICAL_ONLY
For example, 



TextArea instructions = 
 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);
Unlike text fields, text areas do not generate action events when the user
hits return inside the area. Instead, the line is broken and the caret moves on
to the next row. 



However, the getText()
method does return the contents of the TextArea,
and the setText() method
does change it. The setEditable()
method lets you determine whether or not, the user can modify the contents of a
TextField. If these methods
sound familiar it's because they're both inherited from the common superclass
of TextField and TextArea, TextComponent.



Furthermore, you can append text to a TextArea
with the append() method,
insert text into the middle of a TextArea
with the insert() method,
and replace a block of text with the replaceRange()
method:



public void insert(String text, int position)
public void append(String text)  
public void replaceRange(String text, int start, int end)




TextComponent
Both TextArea and TextField are subclasses of java.awt.TextComponent. This class
contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable().
The TextComponent class also
defines methods for manipulating the selection and the caret and for processing
TextEvents. 



The selection is used for copy and paste and other purposes. The first
character in a TextComponent
is character 0; the second is character 1, and so on.



  public int    getSelectionStart()
  public void   setSelectionStart(int selectionStart)
  public int    getSelectionEnd()
  public void   setSelectionEnd(int selectionEnd)
  public void   select(int selectionStart, int selectionEnd)
  public void   selectAll()
  public String getSelectedText()
The caret is the insertion point. It's where text appears when the user
types. There are two methods to adjust it: 



  public void setCaretPosition(int position)
  public int  getCaretPosition()

TextEvents
Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the
component changes. This is more or less every time the user hits a key in the
component. 



The java.awt.event.TextListener
interface defines a single method, textValueChanged():



public void textValueChanged(TextEvent te)
You register a TextListener
with a TextComponent by
calling the component's addTextListener()
method. For example, 



TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set the text as
you need it. It's really quite rare that you need to process it character by
character. 



A TextListener can be
removed by calling removeTextListener().



public void
removeTextListener(TextListener tl)




java.awt.Canvas
The java.awt.Canvas class
is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week.
The Canvas class has only
three methods: 



  public Canvas()
  public void addNotify()
  public void paint(Graphics g)
You generally won't instantiate a canvas directly. Instead you'll subclass
it and override the paint()
method in your subclass to draw the picture you want. 



For example the following Canvas
draws a big red oval you can add to your applet.



import java.awt.*;
 
public class RedOval extends Canvas {
 
  public void paint(Graphics g) {
  
    Dimension d = this.getSize();
    g.setColor(Color.red);
    g.fillOval(0, 0, d.width, d.height);
      
  }
  
  public Dimension getMinimumSize() {
    return new Dimension(50, 100);  
  }
 
  public Dimension getPreferredSize() {
    return new Dimension(150, 300);  
  }
 
  public Dimension getMaximumSize() {
    return new Dimension(200, 400);  
  }
 
}
Any applet that uses components should not also override paint(). Doing so will have unexpected
effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its
paint() method.



Custom canvases are added to applets just like any other component. For
example,



  public void init() {
    this.add(new RedOval());
  }
Canvases themselves do not normally fire any events. Next week, we'll see
how to change that in the subclasses. 




An alternate approach
import java.awt.*;
 
 
public class ColoredOval extends Canvas {
 
  public ColoredOval() {
    this(Color.RED, 100, 100);
  }
 
  public ColoredOval(Color c) {
    this(c, 100, 100);
  }
 
  public ColoredOval(int width, int height) {
    this(Color.RED, width, height);
  }
 
  public ColoredOval(Color c, int width, int height) {
    this.setColor(c);
    this.setSize(width, height);
  }
 
  public void paint(Graphics g) {  
    Dimension d = this.getSize();
    g.fillOval(0, 0, d.width, d.height);
  }
 
}
This is almost but not quite the same effect as the previous applet. (It's a
little less resizeable.) 




java.awt.Choice
The java.awt.Choice class
implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu
with no fixed position. It pops up when the user clicks 




and holds the right mouse button.) 




Creating a choice menu is a little more complex than creating the other user
interface components you've seen. There's an extra step, adding the menu items
to the menu. That is the five steps are




Declare the Choice 
Allocate the Choice 
Add the menu items to the Choice 
Add the Choice to the layout 
Add an ItemListener to the Choice 

For example 



 public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    add(ch);
 
  }   

Methods of java.awt.Choice
The Choice class has a
number of methods to add, remove, and return different items from the list. The
list starts counting at 0. 



  public int    getItemCount()
  public String getItem(int index)
  public void   add(String item)
  public void   addItem(String item)
  public void   insert(String item, int position)
  public void   remove(String item)
  public void   remove(int position)
  public void   removeAll()
However, most of the item you'll just build the Choice when the applet starts up, and
not modify it later. 



These methods get or set the current selected item in the Choice, that is the item that's shown.



  public void     removeAll()
  public String   getSelectedItem()
  public Object[] getSelectedObjects()
  public int      getSelectedIndex()
  public void     select(int position)
  public void     select(String item)




ItemListeners
When the user changes the selected item in a Choice, the Choice
fires two ItemListener
events, one to indicate that the original selection has been deselected and the
other to indicate that a new selection has been made. You can process these
events by registering an ItemListener
object with your Choice. 



You do not always need to do this. It is not uncommon to only check the
value of a Choice when some
other event occurs like a Button
press.



For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user
makes a selection, the applet beeps that many times.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class MultiBeep extends Applet {
  
  public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    this.add(ch);
    ch.addItemListener(new BeepItem());
 
  }    
 
}
 
 
class BeepItem implements ItemListener {
 
  public void itemStateChanged(ItemEvent ie) {
 
    if (ie.getStateChange() == ItemEvent.SELECTED) {
      String name = (String) ie.getItem();
      Toolkit tk = Toolkit.getDefaultToolkit();
      try {
        int n = Integer.parseInt(name);
        for (int i = 0; i < n; i++) tk.beep();
      }
      catch (Exception e) {
        tk.beep();
      }
    }
 
  }
 
}

The BeepItem
class implements the ItemListener
interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only
beeps if an item was selected. The available convenience constants you can
check are: 
ItemEvent.DESELECTED 
ItemEvent.ITEM_FIRST 
ItemEvent.ITEM_LAST 
ItemEvent.ITEM_STATE_CHANGED 
ItemEvent.SELECTED

The ItemEvent.getItem()
method is used to retrieve the actual selected item.




java.awt.Checkbox
Check boxes are used to select a boolean
value. Each Checkbox has a
label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label
"Anchovies" would be checked if the user wants anchovies on their
pizza and unchecked if they don't. 







Checkboxes are often used to select from a list of possible choices when as
few selections as zero or as many as everything on the list may be made. Adding
a Checkbox to an applet is
simple. Just declare it, construct it and add it.



  Checkbox c c = new Checkbox("Pepperoni"));
  add(c);
As usual these steps may be combined into the single line 



add(new
Checkbox("Pepperoni"));



By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the
following constructor instead:



add(new Checkbox("Pepperoni",
null, true));



The null is a reference
to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.



Every Checkbox has a boolean value, either true or false. When the Checkbox
is checked that value is true.
When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean
b) methods. For example



  private void handleCheckbox(Checkbox c) {
  
    if (c.getState()) price += 0.50;
    else price -= 0.50;
  
  }

Checkbox Events
When the a Checkbox
changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore
this event. Instead you manually check the state of a Checkbox when you need to know it.
However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. 



An ItemEvent is exactly
the same as the item event fired by a Choice.
In fact item events are used to indicate selections or deselections in any sort
of list including checkboxes, radio buttons, choices, and lists.



For example, the following program is an applet that asks the age-old
question, "What do you want on your pizza?" When an ingredient is
checked the price of the pizza goes up by fifty cents. When an ingredient is
unchecked fifty cents is taken off. The price is shown in a TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class Ingredients extends Applet {
 
  private TextField display;
  private double price = 7.00;
 
  public void init() {
  
    this.add(new Label("What do you want on your pizza?", Label.CENTER));
      
    Pricer p = new Pricer(this);
    Checkbox pepperoni = new Checkbox("Pepperoni");
    this.add(pepperoni);
    pepperoni.addItemListener(p);
    Checkbox olives = new Checkbox("Olives");
    olives.addItemListener(p);
    this.add(olives);
    Checkbox onions = new Checkbox("Onions");
    onions.addItemListener(p);
    this.add(onions);
    Checkbox sausage = new Checkbox("Sausage");
    sausage.addItemListener(p);
    this.add(sausage);
    Checkbox peppers = new Checkbox("Peppers");
    peppers.addItemListener(p);
    this.add(peppers);
    Checkbox extraCheese = new Checkbox("Extra Cheese");
    extraCheese.addItemListener(p);
    this.add(extraCheese);
    Checkbox ham = new Checkbox("Ham");
    ham.addItemListener(p);
    this.add(ham);
    Checkbox pineapple = new Checkbox("Pineapple");
    pineapple.addItemListener(p);
    this.add(pineapplec);
    Checkbox anchovies = new Checkbox("Anchovies");
    anchovies.addItemListener(p);
    this.add(anchovies);
 
    this.display = new TextField(String.valueOf(price));
    // so people can't change the price of the pizza
    display.setEditable(false); 
    this.add(display);
    
  }
  
  public void setPrice(double price) {
    this.price = price;
    display.setText(String.valueOf(price));
  }
  
  public double getPrice() {
    return this.price;
  }
  
}
 
class Pricer implements ItemListener {
 
  private Ingredients out;
 
  public Pricer(Ingredients out) {
    this.out = out;
  }
  
  public void itemStateChanged(ItemEvent ie) {
  
    double price = out.getPrice();
    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;
    else price -= 0.50;
    // Change the price
    out.setPrice(price);
  
  }
 
}

java.awt.CheckboxGroup
Checkbox groups are collections of checkboxes with the special property that
no more than one checkbox in the same group can be selected at a time. The
checkboxes in a CheckboxGroup
are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked
simultaneously. When the user checks one, all others are unchecked
automatically. 



The constructor for a CheckboxGroup
is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since
checkbox groups are themselves not user-interface widgets, just ways of
arranging checkboxes.



CheckboxGroup cbg = new
CheckboxGroup();



To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.



public Checkbox(String label,
CheckboxGroup cbg, boolean checked)



The label is the label for this Checkbox.
The CheckboxGroup is the
group you want this Checkbox
to belong to and must already exist.



At any time, you can get or set the selected Checkbox with these two methods:



  public Checkbox getSelectedCheckbox()
  public void setSelectedCheckbox(Checkbox box)




java.awt.CheckboxGroup example
The following program asks the customer how they're going to pay for their
pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may
want both anchovies and pineapple on their pizza, but they're unlikely to pay
with both Visa and American Express. 













import java.applet.*;    
import java.awt.*;
 
public class PaymentMethod extends Applet {
 
  public void init() {
    this.add(new Label("How will you pay for your pizza?"));
    CheckboxGroup cbg = new CheckboxGroup();
    this.add(new Checkbox("Visa", cbg, false));
    this.add(new Checkbox("Mastercard", cbg, false));
    this.add(new Checkbox("American Express", cbg, false));
    this.add(new Checkbox("Discover", cbg, false));
    this.add(new Checkbox("Cash", cbg, true)); // the default
  }
  
}
There isn't any action in this simple example applet. If you need to add
action as radio buttons are checked and unchecked, you do it just the same as
for any other Checkbox. 




java.awt.List
Scrolling lists are useful for storing long lists of things one to a line.
The things in the list are called items, but each one is just a String. For
example, 








List Methods
You create a new List
with one of these three constructors: 



  public List()
  public List(int numLines)
  public List(int numLines, boolean allowMultipleSelections)
For example, 



List l = new List(8, true);



numLines is the number of
items you want to be visible in the scrolling list. It is not necessarily the
same as the number of items in the list which is limited only by available
memory. allowMultipleSelections
says whether the user is allowed to select more than one item at once
(typically by Shift-clicking).



The following methods add items at the end of the list:



  public void add(String item)
  public void addItem(String item)
These two methods add items at the specified position in the list. 



  public void add(String item, int index)
  public void addItem(String item, int index)
The following methods remove items from the List: 



  public void removeAll()
  public void remove(String item)
  public void remove(int position)
  public void delItem(int position)

These methods allow you to retrive particular items from the
List: 
  public int getItemCount()
  public String getItem(int index)
  public String[] getItems()
You ran also replace a particular item: 



 public void replaceItem(String newValue, int index)
These methods allow you to determine which item the user has selected: 



  public int      getSelectedIndex()
  public int[]    getSelectedIndexes()
  public String   getSelectedItem()
  public String[] getSelectedItems()
  public Object[] getSelectedObjects()
If a list allows multiple selections, you should use the plural forms of the
above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). 



  public boolean isMultipleMode()
  public void    setMultipleMode(boolean b)
These methods allow you to manipulate the selection: 



  public void    select(int index)
  public void    deselect(int index)
  public boolean isIndexSelected(int index)
These two methods determine whether an item at a particular index is
currently visible in the List box:



  public int  getVisibleIndex()
  public void makeVisible(int index)




List Events
Lists can fire two separate types of events. When a list item is selected or
deselected, the List fires
an ItemEvent. However, when
the user double clicks on a list item, the List
fires an ActionEvent.
Therefore, you can register both an ItemListener
to process selections and/or an ActionListener
to process double clicks. 



public void addItemListener(ItemListener l)
public void removeItemListener(ItemListener l)
public void addActionListener(ActionListener l)
public void removeActionListener(ActionListener l)
The action command in the ActionEvent
is the list item which was double clicked. 




java.awt.Scrollbar
Lists, TextAreas, and ScrollPanes come with ready made
scrollbars. However if you want to scroll any other object you'll have to use a
java.awt.Scrollbar.
Scrollbars have many uses. At their most basic they're used for moving the
visible area. They can also be used to set a value between two numbers. Or they
can be used to flip through a number of screens as in a database operation that
looks at successive records. 



There are three constructors:



public Scrollbar()
public Scrollbar(int orientation)
public Scrollbar(int orientation, int value, int visible, int min, int max)
The orientation argument
is one of the mnemonic constants, Scrollbar.HORIZONTAL
or Scrollbar.VERTICAL. As
you expect this determines whether the Scrollbar
is laid out from left to right or top to bottom. 



A Scrollbar has an int value at all times. This value will
be between the minimum and
the maximum value set by the
last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.



Finally visible
represents the size of the visible portion of the scrollable area in pixels.
The Scrollbar uses this when
moving up or down a page.



A Scrollbar fires an
adjustment event when its value changes. You register an adjustment listener to
catch this event. This class needs an adjustmentValueChanged()
method with this signature:



public void
adjustmentValueChanged(AdjustmentEvent e)



The following program is an applet that changes the number in a TextField between 1 and 100 based on the
position of the thumb (the movable part of the Scrollbar). In a practical application the number would
of course mean something.







import java.applet.*;    
import java.awt.*;
import java.awt.event.*;
 
public class Scrollie extends Applet implements AdjustmentListener {
 
  private TextField t;
  private Scrollbar sb;
 
  public void init() {
    int initialValue = 1;
    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);
    sb.addAdjustmentListener(this);
    this.add(sb);
    this.t = new TextField(4);
    this.t.setText(String.valueOf(initialValue));    
    this.add(t);
  }
  
  public void adjustmentValueChanged(AdjustmentEvent e)
     
    int val = sb.getValue();
    this.t.setText(String.valueOf(val));
    
  }
  
}

Peer vs. Swing Components
I'm not going to talk much about Swing in this course, but most of what I
teach you about the standard AWT components carries over to their Swing
equivalents with only trivial changes. For example, here's yet another way to
write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold
and blue and with a yellow background. 



import java.awt.*;
import javax.swing.*;
 
 
public class SwingCubScout extends JApplet {
 
  public void init() {
  
     JLabel cubScouts = new JLabel("Cub Scouts!");
     cubScouts.setForeground(Color.blue);
     cubScouts.setBackground(Color.yellow);
     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 
     this.getContentPane().add(cubScouts);
     
  }
 
}
This is almost identical to the AWT-based Cub Scout applet, except that I've
imported the javax.swing
package and changed Label to
JLabel and Applet to JApplet. 




Week 6 Exercises

Write an applet that with a
     60 column by 10 row text area that allows the user to type some text. Add
     a button to this applet that clears the text area when it's pressed. 


Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.

Rewrite the payroll problem
     from week 2 as an applet. Provide a text field for the number of hours, a
     text field for the pay rate, and a non-editable text field for the output.
     Also provide labels to identify all three text fields and a button to
     calculate the result. 


Don't worry about minimum wage, number of hours in
the week, or other error conditions we checked before. In the event the user
enters data that cannot be interpreted as a number, don't put anything in the
output text field. In a couple of weeks, you'll learn how to bring up an error
dialog to handle these conditions.

Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.
We'll cover them next week




Getting into more fun Graphics



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class ShowColors2 extends JFrame {
   private JButton changeColorButton;
   private Color color = Color.LIGHT_GRAY;
   private Container container;
 
   // set up GUI
   public ShowColors2()
   {
      super( "Using JColorChooser" );
 
      container = getContentPane();
      container.setLayout( new FlowLayout() );
 
      // set up changeColorButton and register its event handler
      changeColorButton = new JButton( "Change Color" );
      changeColorButton.addActionListener(
 
         new ActionListener() {  // anonymous inner class
 
            // display JColorChooser when user clicks button
            public void actionPerformed( ActionEvent event )
            {
               color = JColorChooser.showDialog( 
                  ShowColors2.this, "Choose a color", color );
 
               // set default color, if no color is returned 
               if ( color == null )
                  color = Color.LIGHT_GRAY;
 
               // change content pane's background color
               container.setBackground( color );
            }
 
         } // end anonymous inner class
 
      ); // end call to addActionListener
 
      container.add( changeColorButton );
 
      setSize( 400, 130 );
      setVisible( true );
 
   } // end ShowColor2 constructor
 
   // execute application
   public static void main( String args[] )
   {
      ShowColors2 application = new ShowColors2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
}






import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class Shapes2 extends JFrame {
 
   // set window's title bar String, background color and dimensions
   public Shapes2()
   {
      super( "Drawing 2D Shapes" );
 
      getContentPane().setBackground( Color.WHITE );
      setSize( 400, 400 );
      setVisible( true );
   }
 
   // draw general paths
   public void paint( Graphics g )
   {
      super.paint( g );  // call superclass's paint method
 
      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };
      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };
 
      Graphics2D g2d = ( Graphics2D ) g;
      GeneralPath star = new GeneralPath();  // create GeneralPath object
 
      // set the initial coordinate of the General Path
      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );
 
      // create the star--this does not draw the star
      for ( int count = 1; count < xPoints.length; count++ )
         star.lineTo( xPoints[ count ], yPoints[ count ] );
 
      star.closePath();  // close the shape
 
      g2d.translate( 200, 200 );  // translate the origin to (200, 200)
 
      // rotate around origin and draw stars in random colors
      for ( int count = 1; count <= 20; count++ ) {
         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system
 
         // set random drawing color
         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),
            ( int ) ( Math.random() * 256 ),              
            ( int ) ( Math.random() * 256 ) ) );
 
         g2d.fill( star );  // draw filled star
      }
 
   } // end method paint
 
   // execute application
   public static void main( String args[] )
   {
      Shapes2 application = new Shapes2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
 
  
} 

An example of text fields in Java
The following applet reads text from one TextField
and capitalizes it in another TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction(input, output);
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
}
 
 
class CapitalizerAction implements ActionListener {
 
  private TextField in;
  private TextField out;
 
  public CapitalizerAction(TextField in, TextField out) {
    this.in = in;
    this.out = out;
  }
 
  public void actionPerformed(ActionEvent ae) {
 
    String s = in.getText();
    out.setText(s.toUpperCase());
 
  }
 
}
In this program, a different pattern is used for handling events. The
constructor for the CapitalizerAction
class is used to pass in references to the different components the actionPerformed() method affects. 




An example of text fields in Java
An alternate pattern uses an inner class so the private fields can be
accessed directly.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction();
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
  class CapitalizerAction implements ActionListener {
 
    public void actionPerformed(ActionEvent ae) {
 
      String s = input.getText();
      output.setText(s.toUpperCase());
 
    }
 
  }
 
 
}

TextArea
The java.awt.TextArea
class is a subclass of java.awt.TextComponent
that provides a widget for editing multiple lines of text. It's useful for
input and output.







There are five constructors:



  public TextArea()
  public TextArea(String text)
  public TextArea(int rows, int columns)
  public TextArea(String text, int rows, int columns)
  public TextArea(String text, int rows, int columns, int scrollbars)
Because of the way Java lays out components, you should not use the noargs
constructor. Either start off with a String
or specify the number of rows and columns this area is expected to hold. For
example, 



TextArea address = new TextArea("Type your address here", 5, 80);
By default, TextAreas don't have scrollbars. However you can add them by
passing one of these constants to the constructor: 



TextArea.SCROLLBARS_BOTH 
TextArea.SCROLLBARS_HORIZONTAL_ONLY 
TextArea.SCROLLBARS_NONE 
TextArea.SCROLLBARS_VERTICAL_ONLY
For example, 



TextArea instructions = 
 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);
Unlike text fields, text areas do not generate action events when the user
hits return inside the area. Instead, the line is broken and the caret moves on
to the next row. 



However, the getText()
method does return the contents of the TextArea,
and the setText() method
does change it. The setEditable()
method lets you determine whether or not, the user can modify the contents of a
TextField. If these methods
sound familiar it's because they're both inherited from the common superclass
of TextField and TextArea, TextComponent.



Furthermore, you can append text to a TextArea
with the append() method,
insert text into the middle of a TextArea
with the insert() method,
and replace a block of text with the replaceRange()
method:



public void insert(String text, int position)
public void append(String text)  
public void replaceRange(String text, int start, int end)




TextComponent
Both TextArea and TextField are subclasses of java.awt.TextComponent. This class
contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable().
The TextComponent class also
defines methods for manipulating the selection and the caret and for processing
TextEvents. 



The selection is used for copy and paste and other purposes. The first
character in a TextComponent
is character 0; the second is character 1, and so on.



  public int    getSelectionStart()
  public void   setSelectionStart(int selectionStart)
  public int    getSelectionEnd()
  public void   setSelectionEnd(int selectionEnd)
  public void   select(int selectionStart, int selectionEnd)
  public void   selectAll()
  public String getSelectedText()
The caret is the insertion point. It's where text appears when the user
types. There are two methods to adjust it: 



  public void setCaretPosition(int position)
  public int  getCaretPosition()

TextEvents
Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the
component changes. This is more or less every time the user hits a key in the
component. 



The java.awt.event.TextListener
interface defines a single method, textValueChanged():



public void textValueChanged(TextEvent te)
You register a TextListener
with a TextComponent by
calling the component's addTextListener()
method. For example, 



TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set the text as
you need it. It's really quite rare that you need to process it character by
character. 



A TextListener can be
removed by calling removeTextListener().



public void
removeTextListener(TextListener tl)




java.awt.Canvas
The java.awt.Canvas class
is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week.
The Canvas class has only
three methods: 



  public Canvas()
  public void addNotify()
  public void paint(Graphics g)
You generally won't instantiate a canvas directly. Instead you'll subclass
it and override the paint()
method in your subclass to draw the picture you want. 



For example the following Canvas
draws a big red oval you can add to your applet.



import java.awt.*;
 
public class RedOval extends Canvas {
 
  public void paint(Graphics g) {
  
    Dimension d = this.getSize();
    g.setColor(Color.red);
    g.fillOval(0, 0, d.width, d.height);
      
  }
  
  public Dimension getMinimumSize() {
    return new Dimension(50, 100);  
  }
 
  public Dimension getPreferredSize() {
    return new Dimension(150, 300);  
  }
 
  public Dimension getMaximumSize() {
    return new Dimension(200, 400);  
  }
 
}
Any applet that uses components should not also override paint(). Doing so will have unexpected
effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its
paint() method.



Custom canvases are added to applets just like any other component. For
example,



  public void init() {
    this.add(new RedOval());
  }
Canvases themselves do not normally fire any events. Next week, we'll see
how to change that in the subclasses. 




An alternate approach
import java.awt.*;
 
 
public class ColoredOval extends Canvas {
 
  public ColoredOval() {
    this(Color.RED, 100, 100);
  }
 
  public ColoredOval(Color c) {
    this(c, 100, 100);
  }
 
  public ColoredOval(int width, int height) {
    this(Color.RED, width, height);
  }
 
  public ColoredOval(Color c, int width, int height) {
    this.setColor(c);
    this.setSize(width, height);
  }
 
  public void paint(Graphics g) {  
    Dimension d = this.getSize();
    g.fillOval(0, 0, d.width, d.height);
  }
 
}
This is almost but not quite the same effect as the previous applet. (It's a
little less resizeable.) 




java.awt.Choice
The java.awt.Choice class
implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu
with no fixed position. It pops up when the user clicks 




and holds the right mouse button.) 




Creating a choice menu is a little more complex than creating the other user
interface components you've seen. There's an extra step, adding the menu items
to the menu. That is the five steps are




Declare the Choice 
Allocate the Choice 
Add the menu items to the Choice 
Add the Choice to the layout 
Add an ItemListener to the Choice 

For example 



 public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    add(ch);
 
  }   

Methods of java.awt.Choice
The Choice class has a
number of methods to add, remove, and return different items from the list. The
list starts counting at 0. 



  public int    getItemCount()
  public String getItem(int index)
  public void   add(String item)
  public void   addItem(String item)
  public void   insert(String item, int position)
  public void   remove(String item)
  public void   remove(int position)
  public void   removeAll()
However, most of the item you'll just build the Choice when the applet starts up, and
not modify it later. 



These methods get or set the current selected item in the Choice, that is the item that's shown.



  public void     removeAll()
  public String   getSelectedItem()
  public Object[] getSelectedObjects()
  public int      getSelectedIndex()
  public void     select(int position)
  public void     select(String item)




ItemListeners
When the user changes the selected item in a Choice, the Choice
fires two ItemListener
events, one to indicate that the original selection has been deselected and the
other to indicate that a new selection has been made. You can process these
events by registering an ItemListener
object with your Choice. 



You do not always need to do this. It is not uncommon to only check the
value of a Choice when some
other event occurs like a Button
press.



For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user
makes a selection, the applet beeps that many times.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class MultiBeep extends Applet {
  
  public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    this.add(ch);
    ch.addItemListener(new BeepItem());
 
  }    
 
}
 
 
class BeepItem implements ItemListener {
 
  public void itemStateChanged(ItemEvent ie) {
 
    if (ie.getStateChange() == ItemEvent.SELECTED) {
      String name = (String) ie.getItem();
      Toolkit tk = Toolkit.getDefaultToolkit();
      try {
        int n = Integer.parseInt(name);
        for (int i = 0; i < n; i++) tk.beep();
      }
      catch (Exception e) {
        tk.beep();
      }
    }
 
  }
 
}

The BeepItem
class implements the ItemListener
interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only
beeps if an item was selected. The available convenience constants you can
check are: 
ItemEvent.DESELECTED 
ItemEvent.ITEM_FIRST 
ItemEvent.ITEM_LAST 
ItemEvent.ITEM_STATE_CHANGED 
ItemEvent.SELECTED

The ItemEvent.getItem()
method is used to retrieve the actual selected item.




java.awt.Checkbox
Check boxes are used to select a boolean
value. Each Checkbox has a
label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label
"Anchovies" would be checked if the user wants anchovies on their
pizza and unchecked if they don't. 







Checkboxes are often used to select from a list of possible choices when as
few selections as zero or as many as everything on the list may be made. Adding
a Checkbox to an applet is
simple. Just declare it, construct it and add it.



  Checkbox c c = new Checkbox("Pepperoni"));
  add(c);
As usual these steps may be combined into the single line 



add(new
Checkbox("Pepperoni"));



By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the
following constructor instead:



add(new Checkbox("Pepperoni",
null, true));



The null is a reference
to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.



Every Checkbox has a boolean value, either true or false. When the Checkbox
is checked that value is true.
When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean
b) methods. For example



  private void handleCheckbox(Checkbox c) {
  
    if (c.getState()) price += 0.50;
    else price -= 0.50;
  
  }

Checkbox Events
When the a Checkbox
changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore
this event. Instead you manually check the state of a Checkbox when you need to know it.
However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. 



An ItemEvent is exactly
the same as the item event fired by a Choice.
In fact item events are used to indicate selections or deselections in any sort
of list including checkboxes, radio buttons, choices, and lists.



For example, the following program is an applet that asks the age-old
question, "What do you want on your pizza?" When an ingredient is
checked the price of the pizza goes up by fifty cents. When an ingredient is
unchecked fifty cents is taken off. The price is shown in a TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class Ingredients extends Applet {
 
  private TextField display;
  private double price = 7.00;
 
  public void init() {
  
    this.add(new Label("What do you want on your pizza?", Label.CENTER));
      
    Pricer p = new Pricer(this);
    Checkbox pepperoni = new Checkbox("Pepperoni");
    this.add(pepperoni);
    pepperoni.addItemListener(p);
    Checkbox olives = new Checkbox("Olives");
    olives.addItemListener(p);
    this.add(olives);
    Checkbox onions = new Checkbox("Onions");
    onions.addItemListener(p);
    this.add(onions);
    Checkbox sausage = new Checkbox("Sausage");
    sausage.addItemListener(p);
    this.add(sausage);
    Checkbox peppers = new Checkbox("Peppers");
    peppers.addItemListener(p);
    this.add(peppers);
    Checkbox extraCheese = new Checkbox("Extra Cheese");
    extraCheese.addItemListener(p);
    this.add(extraCheese);
    Checkbox ham = new Checkbox("Ham");
    ham.addItemListener(p);
    this.add(ham);
    Checkbox pineapple = new Checkbox("Pineapple");
    pineapple.addItemListener(p);
    this.add(pineapplec);
    Checkbox anchovies = new Checkbox("Anchovies");
    anchovies.addItemListener(p);
    this.add(anchovies);
 
    this.display = new TextField(String.valueOf(price));
    // so people can't change the price of the pizza
    display.setEditable(false); 
    this.add(display);
    
  }
  
  public void setPrice(double price) {
    this.price = price;
    display.setText(String.valueOf(price));
  }
  
  public double getPrice() {
    return this.price;
  }
  
}
 
class Pricer implements ItemListener {
 
  private Ingredients out;
 
  public Pricer(Ingredients out) {
    this.out = out;
  }
  
  public void itemStateChanged(ItemEvent ie) {
  
    double price = out.getPrice();
    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;
    else price -= 0.50;
    // Change the price
    out.setPrice(price);
  
  }
 
}

java.awt.CheckboxGroup
Checkbox groups are collections of checkboxes with the special property that
no more than one checkbox in the same group can be selected at a time. The
checkboxes in a CheckboxGroup
are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked
simultaneously. When the user checks one, all others are unchecked
automatically. 



The constructor for a CheckboxGroup
is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since
checkbox groups are themselves not user-interface widgets, just ways of
arranging checkboxes.



CheckboxGroup cbg = new
CheckboxGroup();



To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.



public Checkbox(String label,
CheckboxGroup cbg, boolean checked)



The label is the label for this Checkbox.
The CheckboxGroup is the
group you want this Checkbox
to belong to and must already exist.



At any time, you can get or set the selected Checkbox with these two methods:



  public Checkbox getSelectedCheckbox()
  public void setSelectedCheckbox(Checkbox box)




java.awt.CheckboxGroup example
The following program asks the customer how they're going to pay for their
pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may
want both anchovies and pineapple on their pizza, but they're unlikely to pay
with both Visa and American Express. 













import java.applet.*;    
import java.awt.*;
 
public class PaymentMethod extends Applet {
 
  public void init() {
    this.add(new Label("How will you pay for your pizza?"));
    CheckboxGroup cbg = new CheckboxGroup();
    this.add(new Checkbox("Visa", cbg, false));
    this.add(new Checkbox("Mastercard", cbg, false));
    this.add(new Checkbox("American Express", cbg, false));
    this.add(new Checkbox("Discover", cbg, false));
    this.add(new Checkbox("Cash", cbg, true)); // the default
  }
  
}
There isn't any action in this simple example applet. If you need to add
action as radio buttons are checked and unchecked, you do it just the same as
for any other Checkbox. 




java.awt.List
Scrolling lists are useful for storing long lists of things one to a line.
The things in the list are called items, but each one is just a String. For
example, 








List Methods
You create a new List
with one of these three constructors: 



  public List()
  public List(int numLines)
  public List(int numLines, boolean allowMultipleSelections)
For example, 



List l = new List(8, true);



numLines is the number of
items you want to be visible in the scrolling list. It is not necessarily the
same as the number of items in the list which is limited only by available
memory. allowMultipleSelections
says whether the user is allowed to select more than one item at once
(typically by Shift-clicking).



The following methods add items at the end of the list:



  public void add(String item)
  public void addItem(String item)
These two methods add items at the specified position in the list. 



  public void add(String item, int index)
  public void addItem(String item, int index)
The following methods remove items from the List: 



  public void removeAll()
  public void remove(String item)
  public void remove(int position)
  public void delItem(int position)

These methods allow you to retrive particular items from the
List: 
  public int getItemCount()
  public String getItem(int index)
  public String[] getItems()
You ran also replace a particular item: 



 public void replaceItem(String newValue, int index)
These methods allow you to determine which item the user has selected: 



  public int      getSelectedIndex()
  public int[]    getSelectedIndexes()
  public String   getSelectedItem()
  public String[] getSelectedItems()
  public Object[] getSelectedObjects()
If a list allows multiple selections, you should use the plural forms of the
above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). 



  public boolean isMultipleMode()
  public void    setMultipleMode(boolean b)
These methods allow you to manipulate the selection: 



  public void    select(int index)
  public void    deselect(int index)
  public boolean isIndexSelected(int index)
These two methods determine whether an item at a particular index is
currently visible in the List box:



  public int  getVisibleIndex()
  public void makeVisible(int index)




List Events
Lists can fire two separate types of events. When a list item is selected or
deselected, the List fires
an ItemEvent. However, when
the user double clicks on a list item, the List
fires an ActionEvent.
Therefore, you can register both an ItemListener
to process selections and/or an ActionListener
to process double clicks. 



public void addItemListener(ItemListener l)
public void removeItemListener(ItemListener l)
public void addActionListener(ActionListener l)
public void removeActionListener(ActionListener l)
The action command in the ActionEvent
is the list item which was double clicked. 




java.awt.Scrollbar
Lists, TextAreas, and ScrollPanes come with ready made
scrollbars. However if you want to scroll any other object you'll have to use a
java.awt.Scrollbar.
Scrollbars have many uses. At their most basic they're used for moving the
visible area. They can also be used to set a value between two numbers. Or they
can be used to flip through a number of screens as in a database operation that
looks at successive records. 



There are three constructors:



public Scrollbar()
public Scrollbar(int orientation)
public Scrollbar(int orientation, int value, int visible, int min, int max)
The orientation argument
is one of the mnemonic constants, Scrollbar.HORIZONTAL
or Scrollbar.VERTICAL. As
you expect this determines whether the Scrollbar
is laid out from left to right or top to bottom. 



A Scrollbar has an int value at all times. This value will
be between the minimum and
the maximum value set by the
last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.



Finally visible
represents the size of the visible portion of the scrollable area in pixels.
The Scrollbar uses this when
moving up or down a page.



A Scrollbar fires an
adjustment event when its value changes. You register an adjustment listener to
catch this event. This class needs an adjustmentValueChanged()
method with this signature:



public void
adjustmentValueChanged(AdjustmentEvent e)



The following program is an applet that changes the number in a TextField between 1 and 100 based on the
position of the thumb (the movable part of the Scrollbar). In a practical application the number would
of course mean something.







import java.applet.*;    
import java.awt.*;
import java.awt.event.*;
 
public class Scrollie extends Applet implements AdjustmentListener {
 
  private TextField t;
  private Scrollbar sb;
 
  public void init() {
    int initialValue = 1;
    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);
    sb.addAdjustmentListener(this);
    this.add(sb);
    this.t = new TextField(4);
    this.t.setText(String.valueOf(initialValue));    
    this.add(t);
  }
  
  public void adjustmentValueChanged(AdjustmentEvent e)
     
    int val = sb.getValue();
    this.t.setText(String.valueOf(val));
    
  }
  
}

Peer vs. Swing Components
I'm not going to talk much about Swing in this course, but most of what I
teach you about the standard AWT components carries over to their Swing
equivalents with only trivial changes. For example, here's yet another way to
write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold
and blue and with a yellow background. 



import java.awt.*;
import javax.swing.*;
 
 
public class SwingCubScout extends JApplet {
 
  public void init() {
  
     JLabel cubScouts = new JLabel("Cub Scouts!");
     cubScouts.setForeground(Color.blue);
     cubScouts.setBackground(Color.yellow);
     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 
     this.getContentPane().add(cubScouts);
     
  }
 
}
This is almost identical to the AWT-based Cub Scout applet, except that I've
imported the javax.swing
package and changed Label to
JLabel and Applet to JApplet. 




Week 6 Exercises

Write an applet that with a
     60 column by 10 row text area that allows the user to type some text. Add
     a button to this applet that clears the text area when it's pressed. 


Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.

Rewrite the payroll problem
     from week 2 as an applet. Provide a text field for the number of hours, a
     text field for the pay rate, and a non-editable text field for the output.
     Also provide labels to identify all three text fields and a button to
     calculate the result. 


Don't worry about minimum wage, number of hours in
the week, or other error conditions we checked before. In the event the user
enters data that cannot be interpreted as a number, don't put anything in the
output text field. In a couple of weeks, you'll learn how to bring up an error
dialog to handle these conditions.

Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.
We'll cover them next week




Getting into more fun Graphics



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class ShowColors2 extends JFrame {
   private JButton changeColorButton;
   private Color color = Color.LIGHT_GRAY;
   private Container container;
 
   // set up GUI
   public ShowColors2()
   {
      super( "Using JColorChooser" );
 
      container = getContentPane();
      container.setLayout( new FlowLayout() );
 
      // set up changeColorButton and register its event handler
      changeColorButton = new JButton( "Change Color" );
      changeColorButton.addActionListener(
 
         new ActionListener() {  // anonymous inner class
 
            // display JColorChooser when user clicks button
            public void actionPerformed( ActionEvent event )
            {
               color = JColorChooser.showDialog( 
                  ShowColors2.this, "Choose a color", color );
 
               // set default color, if no color is returned 
               if ( color == null )
                  color = Color.LIGHT_GRAY;
 
               // change content pane's background color
               container.setBackground( color );
            }
 
         } // end anonymous inner class
 
      ); // end call to addActionListener
 
      container.add( changeColorButton );
 
      setSize( 400, 130 );
      setVisible( true );
 
   } // end ShowColor2 constructor
 
   // execute application
   public static void main( String args[] )
   {
      ShowColors2 application = new ShowColors2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
}






import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class Shapes2 extends JFrame {
 
   // set window's title bar String, background color and dimensions
   public Shapes2()
   {
      super( "Drawing 2D Shapes" );
 
      getContentPane().setBackground( Color.WHITE );
      setSize( 400, 400 );
      setVisible( true );
   }
 
   // draw general paths
   public void paint( Graphics g )
   {
      super.paint( g );  // call superclass's paint method
 
      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };
      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };
 
      Graphics2D g2d = ( Graphics2D ) g;
      GeneralPath star = new GeneralPath();  // create GeneralPath object
 
      // set the initial coordinate of the General Path
      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );
 
      // create the star--this does not draw the star
      for ( int count = 1; count < xPoints.length; count++ )
         star.lineTo( xPoints[ count ], yPoints[ count ] );
 
      star.closePath();  // close the shape
 
      g2d.translate( 200, 200 );  // translate the origin to (200, 200)
 
      // rotate around origin and draw stars in random colors
      for ( int count = 1; count <= 20; count++ ) {
         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system
 
         // set random drawing color
         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),
            ( int ) ( Math.random() * 256 ),              
            ( int ) ( Math.random() * 256 ) ) );
 
         g2d.fill( star );  // draw filled star
      }
 
   } // end method paint
 
   // execute application
   public static void main( String args[] )
   {
      Shapes2 application = new Shapes2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
  
} 

An example of text fields in Java
The following applet reads text from one TextField
and capitalizes it in another TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction(input, output);
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
}
 
 
class CapitalizerAction implements ActionListener {
 
  private TextField in;
  private TextField out;
 
  public CapitalizerAction(TextField in, TextField out) {
    this.in = in;
    this.out = out;
  }
 
  public void actionPerformed(ActionEvent ae) {
 
    String s = in.getText();
    out.setText(s.toUpperCase());
 
  }
 
}
In this program, a different pattern is used for handling events. The
constructor for the CapitalizerAction
class is used to pass in references to the different components the actionPerformed() method affects. 




An example of text fields in Java
An alternate pattern uses an inner class so the private fields can be
accessed directly.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction();
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
  class CapitalizerAction implements ActionListener {
 
    public void actionPerformed(ActionEvent ae) {
 
      String s = input.getText();
      output.setText(s.toUpperCase());
 
    }
 
  }
 
 
}

TextArea
The java.awt.TextArea
class is a subclass of java.awt.TextComponent
that provides a widget for editing multiple lines of text. It's useful for
input and output.







There are five constructors:



  public TextArea()
  public TextArea(String text)
  public TextArea(int rows, int columns)
  public TextArea(String text, int rows, int columns)
  public TextArea(String text, int rows, int columns, int scrollbars)
Because of the way Java lays out components, you should not use the noargs
constructor. Either start off with a String
or specify the number of rows and columns this area is expected to hold. For
example, 



TextArea address = new TextArea("Type your address here", 5, 80);
By default, TextAreas don't have scrollbars. However you can add them by
passing one of these constants to the constructor: 



TextArea.SCROLLBARS_BOTH 
TextArea.SCROLLBARS_HORIZONTAL_ONLY 
TextArea.SCROLLBARS_NONE 
TextArea.SCROLLBARS_VERTICAL_ONLY
For example, 



TextArea instructions = 
 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);
Unlike text fields, text areas do not generate action events when the user
hits return inside the area. Instead, the line is broken and the caret moves on
to the next row. 



However, the getText()
method does return the contents of the TextArea,
and the setText() method
does change it. The setEditable()
method lets you determine whether or not, the user can modify the contents of a
TextField. If these methods
sound familiar it's because they're both inherited from the common superclass
of TextField and TextArea, TextComponent.



Furthermore, you can append text to a TextArea
with the append() method,
insert text into the middle of a TextArea
with the insert() method,
and replace a block of text with the replaceRange()
method:



public void insert(String text, int position)
public void append(String text)  
public void replaceRange(String text, int start, int end)




TextComponent
Both TextArea and TextField are subclasses of java.awt.TextComponent. This class
contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable().
The TextComponent class also
defines methods for manipulating the selection and the caret and for processing
TextEvents. 



The selection is used for copy and paste and other purposes. The first
character in a TextComponent
is character 0; the second is character 1, and so on.



  public int    getSelectionStart()
  public void   setSelectionStart(int selectionStart)
  public int    getSelectionEnd()
  public void   setSelectionEnd(int selectionEnd)
  public void   select(int selectionStart, int selectionEnd)
  public void   selectAll()
  public String getSelectedText()
The caret is the insertion point. It's where text appears when the user
types. There are two methods to adjust it: 



  public void setCaretPosition(int position)
  public int  getCaretPosition()

TextEvents
Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the
component changes. This is more or less every time the user hits a key in the
component. 



The java.awt.event.TextListener
interface defines a single method, textValueChanged():



public void textValueChanged(TextEvent te)
You register a TextListener
with a TextComponent by
calling the component's addTextListener()
method. For example, 



TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set the text as
you need it. It's really quite rare that you need to process it character by
character. 



A TextListener can be
removed by calling removeTextListener().



public void
removeTextListener(TextListener tl)




java.awt.Canvas
The java.awt.Canvas class
is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week.
The Canvas class has only
three methods: 



  public Canvas()
  public void addNotify()
  public void paint(Graphics g)
You generally won't instantiate a canvas directly. Instead you'll subclass
it and override the paint()
method in your subclass to draw the picture you want. 



For example the following Canvas
draws a big red oval you can add to your applet.



import java.awt.*;
 
public class RedOval extends Canvas {
 
  public void paint(Graphics g) {
  
    Dimension d = this.getSize();
    g.setColor(Color.red);
    g.fillOval(0, 0, d.width, d.height);
      
  }
  
  public Dimension getMinimumSize() {
    return new Dimension(50, 100);  
  }
 
  public Dimension getPreferredSize() {
    return new Dimension(150, 300);  
  }
 
  public Dimension getMaximumSize() {
    return new Dimension(200, 400);  
  }
 
}
Any applet that uses components should not also override paint(). Doing so will have unexpected
effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its
paint() method.



Custom canvases are added to applets just like any other component. For
example,



  public void init() {
    this.add(new RedOval());
  }
Canvases themselves do not normally fire any events. Next week, we'll see
how to change that in the subclasses. 




An alternate approach
import java.awt.*;
 
 
public class ColoredOval extends Canvas {
 
  public ColoredOval() {
    this(Color.RED, 100, 100);
  }
 
  public ColoredOval(Color c) {
    this(c, 100, 100);
  }
 
  public ColoredOval(int width, int height) {
    this(Color.RED, width, height);
  }
 
  public ColoredOval(Color c, int width, int height) {
    this.setColor(c);
    this.setSize(width, height);
  }
 
  public void paint(Graphics g) {  
    Dimension d = this.getSize();
    g.fillOval(0, 0, d.width, d.height);
  }
 
}
This is almost but not quite the same effect as the previous applet. (It's a
little less resizeable.) 




java.awt.Choice
The java.awt.Choice class
implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu
with no fixed position. It pops up when the user clicks 




and holds the right mouse button.) 




Creating a choice menu is a little more complex than creating the other user
interface components you've seen. There's an extra step, adding the menu items
to the menu. That is the five steps are




Declare the Choice 
Allocate the Choice 
Add the menu items to the Choice 
Add the Choice to the layout 
Add an ItemListener to the Choice 

For example 



 public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    add(ch);
 
  }   

Methods of java.awt.Choice
The Choice class has a
number of methods to add, remove, and return different items from the list. The
list starts counting at 0. 



  public int    getItemCount()
  public String getItem(int index)
  public void   add(String item)
  public void   addItem(String item)
  public void   insert(String item, int position)
  public void   remove(String item)
  public void   remove(int position)
  public void   removeAll()
However, most of the item you'll just build the Choice when the applet starts up, and
not modify it later. 



These methods get or set the current selected item in the Choice, that is the item that's shown.



  public void     removeAll()
  public String   getSelectedItem()
  public Object[] getSelectedObjects()
  public int      getSelectedIndex()
  public void     select(int position)
  public void     select(String item)




ItemListeners
When the user changes the selected item in a Choice, the Choice
fires two ItemListener
events, one to indicate that the original selection has been deselected and the
other to indicate that a new selection has been made. You can process these
events by registering an ItemListener
object with your Choice. 



You do not always need to do this. It is not uncommon to only check the
value of a Choice when some
other event occurs like a Button
press.



For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user
makes a selection, the applet beeps that many times.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class MultiBeep extends Applet {
  
  public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    this.add(ch);
    ch.addItemListener(new BeepItem());
 
  }    
 
}
 
 
class BeepItem implements ItemListener {
 
  public void itemStateChanged(ItemEvent ie) {
 
    if (ie.getStateChange() == ItemEvent.SELECTED) {
      String name = (String) ie.getItem();
      Toolkit tk = Toolkit.getDefaultToolkit();
      try {
        int n = Integer.parseInt(name);
        for (int i = 0; i < n; i++) tk.beep();
      }
      catch (Exception e) {
        tk.beep();
      }
    }
 
  }
 
}

The BeepItem
class implements the ItemListener
interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only
beeps if an item was selected. The available convenience constants you can
check are: 
ItemEvent.DESELECTED 
ItemEvent.ITEM_FIRST 
ItemEvent.ITEM_LAST 
ItemEvent.ITEM_STATE_CHANGED 
ItemEvent.SELECTED

The ItemEvent.getItem()
method is used to retrieve the actual selected item.




java.awt.Checkbox
Check boxes are used to select a boolean
value. Each Checkbox has a
label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label
"Anchovies" would be checked if the user wants anchovies on their
pizza and unchecked if they don't. 







Checkboxes are often used to select from a list of possible choices when as
few selections as zero or as many as everything on the list may be made. Adding
a Checkbox to an applet is
simple. Just declare it, construct it and add it.



  Checkbox c c = new Checkbox("Pepperoni"));
  add(c);
As usual these steps may be combined into the single line 



add(new
Checkbox("Pepperoni"));



By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the
following constructor instead:



add(new Checkbox("Pepperoni",
null, true));



The null is a reference
to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.



Every Checkbox has a boolean value, either true or false. When the Checkbox
is checked that value is true.
When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean
b) methods. For example



  private void handleCheckbox(Checkbox c) {
  
    if (c.getState()) price += 0.50;
    else price -= 0.50;
  
  }

Checkbox Events
When the a Checkbox
changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore
this event. Instead you manually check the state of a Checkbox when you need to know it.
However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. 



An ItemEvent is exactly
the same as the item event fired by a Choice.
In fact item events are used to indicate selections or deselections in any sort
of list including checkboxes, radio buttons, choices, and lists.



For example, the following program is an applet that asks the age-old
question, "What do you want on your pizza?" When an ingredient is
checked the price of the pizza goes up by fifty cents. When an ingredient is
unchecked fifty cents is taken off. The price is shown in a TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class Ingredients extends Applet {
 
  private TextField display;
  private double price = 7.00;
 
  public void init() {
  
    this.add(new Label("What do you want on your pizza?", Label.CENTER));
      
    Pricer p = new Pricer(this);
    Checkbox pepperoni = new Checkbox("Pepperoni");
    this.add(pepperoni);
    pepperoni.addItemListener(p);
    Checkbox olives = new Checkbox("Olives");
    olives.addItemListener(p);
    this.add(olives);
    Checkbox onions = new Checkbox("Onions");
    onions.addItemListener(p);
    this.add(onions);
    Checkbox sausage = new Checkbox("Sausage");
    sausage.addItemListener(p);
    this.add(sausage);
    Checkbox peppers = new Checkbox("Peppers");
    peppers.addItemListener(p);
    this.add(peppers);
    Checkbox extraCheese = new Checkbox("Extra Cheese");
    extraCheese.addItemListener(p);
    this.add(extraCheese);
    Checkbox ham = new Checkbox("Ham");
    ham.addItemListener(p);
    this.add(ham);
    Checkbox pineapple = new Checkbox("Pineapple");
    pineapple.addItemListener(p);
    this.add(pineapplec);
    Checkbox anchovies = new Checkbox("Anchovies");
    anchovies.addItemListener(p);
    this.add(anchovies);
 
    this.display = new TextField(String.valueOf(price));
    // so people can't change the price of the pizza
    display.setEditable(false); 
    this.add(display);
    
  }
  
  public void setPrice(double price) {
    this.price = price;
    display.setText(String.valueOf(price));
  }
  
  public double getPrice() {
    return this.price;
  }
  
}
 
class Pricer implements ItemListener {
 
  private Ingredients out;
 
  public Pricer(Ingredients out) {
    this.out = out;
  }
  
  public void itemStateChanged(ItemEvent ie) {
  
    double price = out.getPrice();
    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;
    else price -= 0.50;
    // Change the price
    out.setPrice(price);
  
  }
 
}

java.awt.CheckboxGroup
Checkbox groups are collections of checkboxes with the special property that
no more than one checkbox in the same group can be selected at a time. The
checkboxes in a CheckboxGroup
are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked
simultaneously. When the user checks one, all others are unchecked
automatically. 



The constructor for a CheckboxGroup
is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since
checkbox groups are themselves not user-interface widgets, just ways of
arranging checkboxes.



CheckboxGroup cbg = new
CheckboxGroup();



To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.



public Checkbox(String label,
CheckboxGroup cbg, boolean checked)



The label is the label for this Checkbox.
The CheckboxGroup is the
group you want this Checkbox
to belong to and must already exist.



At any time, you can get or set the selected Checkbox with these two methods:



  public Checkbox getSelectedCheckbox()
  public void setSelectedCheckbox(Checkbox box)




java.awt.CheckboxGroup example
The following program asks the customer how they're going to pay for their
pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may
want both anchovies and pineapple on their pizza, but they're unlikely to pay
with both Visa and American Express. 













import java.applet.*;    
import java.awt.*;
 
public class PaymentMethod extends Applet {
 
  public void init() {
    this.add(new Label("How will you pay for your pizza?"));
    CheckboxGroup cbg = new CheckboxGroup();
    this.add(new Checkbox("Visa", cbg, false));
    this.add(new Checkbox("Mastercard", cbg, false));
    this.add(new Checkbox("American Express", cbg, false));
    this.add(new Checkbox("Discover", cbg, false));
    this.add(new Checkbox("Cash", cbg, true)); // the default
  }
  
}
There isn't any action in this simple example applet. If you need to add
action as radio buttons are checked and unchecked, you do it just the same as
for any other Checkbox. 




java.awt.List
Scrolling lists are useful for storing long lists of things one to a line.
The things in the list are called items, but each one is just a String. For
example, 








List Methods
You create a new List
with one of these three constructors: 



  public List()
  public List(int numLines)
  public List(int numLines, boolean allowMultipleSelections)
For example, 



List l = new List(8, true);



numLines is the number of
items you want to be visible in the scrolling list. It is not necessarily the
same as the number of items in the list which is limited only by available
memory. allowMultipleSelections
says whether the user is allowed to select more than one item at once
(typically by Shift-clicking).



The following methods add items at the end of the list:



  public void add(String item)
  public void addItem(String item)
These two methods add items at the specified position in the list. 



  public void add(String item, int index)
  public void addItem(String item, int index)
The following methods remove items from the List: 



  public void removeAll()
  public void remove(String item)
  public void remove(int position)
  public void delItem(int position)

These methods allow you to retrive particular items from the
List: 
  public int getItemCount()
  public String getItem(int index)
  public String[] getItems()
You ran also replace a particular item: 



 public void replaceItem(String newValue, int index)
These methods allow you to determine which item the user has selected: 



  public int      getSelectedIndex()
  public int[]    getSelectedIndexes()
  public String   getSelectedItem()
  public String[] getSelectedItems()
  public Object[] getSelectedObjects()
If a list allows multiple selections, you should use the plural forms of the
above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). 



  public boolean isMultipleMode()
  public void    setMultipleMode(boolean b)
These methods allow you to manipulate the selection: 



  public void    select(int index)
  public void    deselect(int index)
  public boolean isIndexSelected(int index)
These two methods determine whether an item at a particular index is
currently visible in the List box:



  public int  getVisibleIndex()
  public void makeVisible(int index)




List Events
Lists can fire two separate types of events. When a list item is selected or
deselected, the List fires
an ItemEvent. However, when
the user double clicks on a list item, the List
fires an ActionEvent.
Therefore, you can register both an ItemListener
to process selections and/or an ActionListener
to process double clicks. 



public void addItemListener(ItemListener l)
public void removeItemListener(ItemListener l)
public void addActionListener(ActionListener l)
public void removeActionListener(ActionListener l)
The action command in the ActionEvent
is the list item which was double clicked. 




java.awt.Scrollbar
Lists, TextAreas, and ScrollPanes come with ready made
scrollbars. However if you want to scroll any other object you'll have to use a
java.awt.Scrollbar.
Scrollbars have many uses. At their most basic they're used for moving the
visible area. They can also be used to set a value between two numbers. Or they
can be used to flip through a number of screens as in a database operation that
looks at successive records. 



There are three constructors:



public Scrollbar()
public Scrollbar(int orientation)
public Scrollbar(int orientation, int value, int visible, int min, int max)
The orientation argument
is one of the mnemonic constants, Scrollbar.HORIZONTAL
or Scrollbar.VERTICAL. As
you expect this determines whether the Scrollbar
is laid out from left to right or top to bottom. 



A Scrollbar has an int value at all times. This value will
be between the minimum and
the maximum value set by the
last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.



Finally visible
represents the size of the visible portion of the scrollable area in pixels.
The Scrollbar uses this when
moving up or down a page.



A Scrollbar fires an
adjustment event when its value changes. You register an adjustment listener to
catch this event. This class needs an adjustmentValueChanged()
method with this signature:



public void
adjustmentValueChanged(AdjustmentEvent e)



The following program is an applet that changes the number in a TextField between 1 and 100 based on the
position of the thumb (the movable part of the Scrollbar). In a practical application the number would
of course mean something.







import java.applet.*;    
import java.awt.*;
import java.awt.event.*;
 
public class Scrollie extends Applet implements AdjustmentListener {
 
  private TextField t;
  private Scrollbar sb;
 
  public void init() {
    int initialValue = 1;
    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);
    sb.addAdjustmentListener(this);
    this.add(sb);
    this.t = new TextField(4);
    this.t.setText(String.valueOf(initialValue));    
    this.add(t);
  }
  
  public void adjustmentValueChanged(AdjustmentEvent e)
     
    int val = sb.getValue();
    this.t.setText(String.valueOf(val));
    
  }
  
}

Peer vs. Swing Components
I'm not going to talk much about Swing in this course, but most of what I
teach you about the standard AWT components carries over to their Swing
equivalents with only trivial changes. For example, here's yet another way to
write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold
and blue and with a yellow background. 



import java.awt.*;
import javax.swing.*;
 
 
public class SwingCubScout extends JApplet {
 
  public void init() {
  
     JLabel cubScouts = new JLabel("Cub Scouts!");
     cubScouts.setForeground(Color.blue);
     cubScouts.setBackground(Color.yellow);
     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 
     this.getContentPane().add(cubScouts);
     
  }
 
}
This is almost identical to the AWT-based Cub Scout applet, except that I've
imported the javax.swing
package and changed Label to
JLabel and Applet to JApplet. 




Week 6 Exercises

Write an applet that with a
     60 column by 10 row text area that allows the user to type some text. Add
     a button to this applet that clears the text area when it's pressed. 


Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.

Rewrite the payroll problem
     from week 2 as an applet. Provide a text field for the number of hours, a
     text field for the pay rate, and a non-editable text field for the output.
     Also provide labels to identify all three text fields and a button to
     calculate the result. 


Don't worry about minimum wage, number of hours in
the week, or other error conditions we checked before. In the event the user
enters data that cannot be interpreted as a number, don't put anything in the
output text field. In a couple of weeks, you'll learn how to bring up an error
dialog to handle these conditions.

Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.
We'll cover them next week




Getting into more fun Graphics



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class ShowColors2 extends JFrame {
   private JButton changeColorButton;
   private Color color = Color.LIGHT_GRAY;
   private Container container;
 
   // set up GUI
   public ShowColors2()
   {
      super( "Using JColorChooser" );
 
      container = getContentPane();
      container.setLayout( new FlowLayout() );
 
      // set up changeColorButton and register its event handler
      changeColorButton = new JButton( "Change Color" );
      changeColorButton.addActionListener(
 
         new ActionListener() {  // anonymous inner class
 
            // display JColorChooser when user clicks button
            public void actionPerformed( ActionEvent event )
            {
               color = JColorChooser.showDialog( 
                  ShowColors2.this, "Choose a color", color );
 
               // set default color, if no color is returned 
               if ( color == null )
                  color = Color.LIGHT_GRAY;
 
               // change content pane's background color
               container.setBackground( color );
            }
 
         } // end anonymous inner class
 
      ); // end call to addActionListener
 
      container.add( changeColorButton );
 
      setSize( 400, 130 );
      setVisible( true );
 
   } // end ShowColor2 constructor
 
   // execute application
   public static void main( String args[] )
   {
      ShowColors2 application = new ShowColors2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
}






import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class Shapes2 extends JFrame {
 
   // set window's title bar String, background color and dimensions
   public Shapes2()
   {
      super( "Drawing 2D Shapes" );
 
      getContentPane().setBackground( Color.WHITE );
      setSize( 400, 400 );
      setVisible( true );
   }
 
   // draw general paths
   public void paint( Graphics g )
   {
      super.paint( g );  // call superclass's paint method
 
      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };
      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };
 
      Graphics2D g2d = ( Graphics2D ) g;
      GeneralPath star = new GeneralPath();  // create GeneralPath object
 
      // set the initial coordinate of the General Path
      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );
 
      // create the star--this does not draw the star
      for ( int count = 1; count < xPoints.length; count++ )
         star.lineTo( xPoints[ count ], yPoints[ count ] );
 
      star.closePath();  // close the shape
 
      g2d.translate( 200, 200 );  // translate the origin to (200, 200)
 
      // rotate around origin and draw stars in random colors
      for ( int count = 1; count <= 20; count++ ) {
         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system
 
         // set random drawing color
         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),
            ( int ) ( Math.random() * 256 ),              
            ( int ) ( Math.random() * 256 ) ) );
 
         g2d.fill( star );  // draw filled star
      }
 
   } // end method paint
 
   // execute application
   public static void main( String args[] )
   {
      Shapes2 application = new Shapes2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
  
} 

An example of text fields in Java
The following applet reads text from one TextField
and capitalizes it in another TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction(input, output);
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
}
 
 
class CapitalizerAction implements ActionListener {
 
  private TextField in;
  private TextField out;
 
  public CapitalizerAction(TextField in, TextField out) {
    this.in = in;
    this.out = out;
  }
 
  public void actionPerformed(ActionEvent ae) {
 
    String s = in.getText();
    out.setText(s.toUpperCase());
 
  }
 
}
In this program, a different pattern is used for handling events. The
constructor for the CapitalizerAction
class is used to pass in references to the different components the actionPerformed() method affects. 




An example of text fields in Java
An alternate pattern uses an inner class so the private fields can be
accessed directly.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction();
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
  class CapitalizerAction implements ActionListener {
 
    public void actionPerformed(ActionEvent ae) {
 
      String s = input.getText();
      output.setText(s.toUpperCase());
 
    }
 
  }
 
 
}

TextArea
The java.awt.TextArea
class is a subclass of java.awt.TextComponent
that provides a widget for editing multiple lines of text. It's useful for
input and output.







There are five constructors:



  public TextArea()
  public TextArea(String text)
  public TextArea(int rows, int columns)
  public TextArea(String text, int rows, int columns)
  public TextArea(String text, int rows, int columns, int scrollbars)
Because of the way Java lays out components, you should not use the noargs
constructor. Either start off with a String
or specify the number of rows and columns this area is expected to hold. For
example, 



TextArea address = new TextArea("Type your address here", 5, 80);
By default, TextAreas don't have scrollbars. However you can add them by
passing one of these constants to the constructor: 



TextArea.SCROLLBARS_BOTH 
TextArea.SCROLLBARS_HORIZONTAL_ONLY 
TextArea.SCROLLBARS_NONE 
TextArea.SCROLLBARS_VERTICAL_ONLY
For example, 



TextArea instructions = 
 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);
Unlike text fields, text areas do not generate action events when the user
hits return inside the area. Instead, the line is broken and the caret moves on
to the next row. 



However, the getText()
method does return the contents of the TextArea,
and the setText() method
does change it. The setEditable()
method lets you determine whether or not, the user can modify the contents of a
TextField. If these methods
sound familiar it's because they're both inherited from the common superclass
of TextField and TextArea, TextComponent.



Furthermore, you can append text to a TextArea
with the append() method,
insert text into the middle of a TextArea
with the insert() method,
and replace a block of text with the replaceRange()
method:



public void insert(String text, int position)
public void append(String text)  
public void replaceRange(String text, int start, int end)




TextComponent
Both TextArea and TextField are subclasses of java.awt.TextComponent. This class
contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable().
The TextComponent class also
defines methods for manipulating the selection and the caret and for processing
TextEvents. 



The selection is used for copy and paste and other purposes. The first
character in a TextComponent
is character 0; the second is character 1, and so on.



  public int    getSelectionStart()
  public void   setSelectionStart(int selectionStart)
  public int    getSelectionEnd()
  public void   setSelectionEnd(int selectionEnd)
  public void   select(int selectionStart, int selectionEnd)
  public void   selectAll()
  public String getSelectedText()
The caret is the insertion point. It's where text appears when the user
types. There are two methods to adjust it: 



  public void setCaretPosition(int position)
  public int  getCaretPosition()

TextEvents
Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the
component changes. This is more or less every time the user hits a key in the
component. 



The java.awt.event.TextListener
interface defines a single method, textValueChanged():



public void textValueChanged(TextEvent te)
You register a TextListener
with a TextComponent by
calling the component's addTextListener()
method. For example, 



TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set the text as
you need it. It's really quite rare that you need to process it character by
character. 



A TextListener can be
removed by calling removeTextListener().



public void
removeTextListener(TextListener tl)




java.awt.Canvas
The java.awt.Canvas class
is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week.
The Canvas class has only
three methods: 



  public Canvas()
  public void addNotify()
  public void paint(Graphics g)
You generally won't instantiate a canvas directly. Instead you'll subclass
it and override the paint()
method in your subclass to draw the picture you want. 



For example the following Canvas
draws a big red oval you can add to your applet.



import java.awt.*;
 
public class RedOval extends Canvas {
 
  public void paint(Graphics g) {
  
    Dimension d = this.getSize();
    g.setColor(Color.red);
    g.fillOval(0, 0, d.width, d.height);
      
  }
  
  public Dimension getMinimumSize() {
    return new Dimension(50, 100);  
  }
 
  public Dimension getPreferredSize() {
    return new Dimension(150, 300);  
  }
 
  public Dimension getMaximumSize() {
    return new Dimension(200, 400);  
  }
 
}
Any applet that uses components should not also override paint(). Doing so will have unexpected
effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its
paint() method.



Custom canvases are added to applets just like any other component. For
example,



  public void init() {
    this.add(new RedOval());
  }
Canvases themselves do not normally fire any events. Next week, we'll see
how to change that in the subclasses. 




An alternate approach
import java.awt.*;
 
 
public class ColoredOval extends Canvas {
 
  public ColoredOval() {
    this(Color.RED, 100, 100);
  }
 
  public ColoredOval(Color c) {
    this(c, 100, 100);
  }
 
  public ColoredOval(int width, int height) {
    this(Color.RED, width, height);
  }
 
  public ColoredOval(Color c, int width, int height) {
    this.setColor(c);
    this.setSize(width, height);
  }
 
  public void paint(Graphics g) {  
    Dimension d = this.getSize();
    g.fillOval(0, 0, d.width, d.height);
  }
 
}
This is almost but not quite the same effect as the previous applet. (It's a
little less resizeable.) 




java.awt.Choice
The java.awt.Choice class
implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu
with no fixed position. It pops up when the user clicks 




and holds the right mouse button.) 




Creating a choice menu is a little more complex than creating the other user
interface components you've seen. There's an extra step, adding the menu items
to the menu. That is the five steps are




Declare the Choice 
Allocate the Choice 
Add the menu items to the Choice 
Add the Choice to the layout 
Add an ItemListener to the Choice 

For example 



 public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    add(ch);
 
  }   

Methods of java.awt.Choice
The Choice class has a
number of methods to add, remove, and return different items from the list. The
list starts counting at 0. 



  public int    getItemCount()
  public String getItem(int index)
  public void   add(String item)
  public void   addItem(String item)
  public void   insert(String item, int position)
  public void   remove(String item)
  public void   remove(int position)
  public void   removeAll()
However, most of the item you'll just build the Choice when the applet starts up, and
not modify it later. 



These methods get or set the current selected item in the Choice, that is the item that's shown.



  public void     removeAll()
  public String   getSelectedItem()
  public Object[] getSelectedObjects()
  public int      getSelectedIndex()
  public void     select(int position)
  public void     select(String item)




ItemListeners
When the user changes the selected item in a Choice, the Choice
fires two ItemListener
events, one to indicate that the original selection has been deselected and the
other to indicate that a new selection has been made. You can process these
events by registering an ItemListener
object with your Choice. 



You do not always need to do this. It is not uncommon to only check the
value of a Choice when some
other event occurs like a Button
press.



For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user
makes a selection, the applet beeps that many times.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class MultiBeep extends Applet {
  
  public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    this.add(ch);
    ch.addItemListener(new BeepItem());
 
  }    
 
}
 
 
class BeepItem implements ItemListener {
 
  public void itemStateChanged(ItemEvent ie) {
 
    if (ie.getStateChange() == ItemEvent.SELECTED) {
      String name = (String) ie.getItem();
      Toolkit tk = Toolkit.getDefaultToolkit();
      try {
        int n = Integer.parseInt(name);
        for (int i = 0; i < n; i++) tk.beep();
      }
      catch (Exception e) {
        tk.beep();
      }
    }
 
  }
 
}

The BeepItem
class implements the ItemListener
interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only
beeps if an item was selected. The available convenience constants you can
check are: 
ItemEvent.DESELECTED 
ItemEvent.ITEM_FIRST 
ItemEvent.ITEM_LAST 
ItemEvent.ITEM_STATE_CHANGED 
ItemEvent.SELECTED

The ItemEvent.getItem()
method is used to retrieve the actual selected item.




java.awt.Checkbox
Check boxes are used to select a boolean
value. Each Checkbox has a
label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label
"Anchovies" would be checked if the user wants anchovies on their
pizza and unchecked if they don't. 







Checkboxes are often used to select from a list of possible choices when as
few selections as zero or as many as everything on the list may be made. Adding
a Checkbox to an applet is
simple. Just declare it, construct it and add it.



  Checkbox c c = new Checkbox("Pepperoni"));
  add(c);
As usual these steps may be combined into the single line 



add(new
Checkbox("Pepperoni"));



By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the
following constructor instead:



add(new Checkbox("Pepperoni",
null, true));



The null is a reference
to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.



Every Checkbox has a boolean value, either true or false. When the Checkbox
is checked that value is true.
When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean
b) methods. For example



  private void handleCheckbox(Checkbox c) {
  
    if (c.getState()) price += 0.50;
    else price -= 0.50;
  
  }

Checkbox Events
When the a Checkbox
changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore
this event. Instead you manually check the state of a Checkbox when you need to know it.
However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. 



An ItemEvent is exactly
the same as the item event fired by a Choice.
In fact item events are used to indicate selections or deselections in any sort
of list including checkboxes, radio buttons, choices, and lists.



For example, the following program is an applet that asks the age-old
question, "What do you want on your pizza?" When an ingredient is
checked the price of the pizza goes up by fifty cents. When an ingredient is
unchecked fifty cents is taken off. The price is shown in a TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class Ingredients extends Applet {
 
  private TextField display;
  private double price = 7.00;
 
  public void init() {
  
    this.add(new Label("What do you want on your pizza?", Label.CENTER));
      
    Pricer p = new Pricer(this);
    Checkbox pepperoni = new Checkbox("Pepperoni");
    this.add(pepperoni);
    pepperoni.addItemListener(p);
    Checkbox olives = new Checkbox("Olives");
    olives.addItemListener(p);
    this.add(olives);
    Checkbox onions = new Checkbox("Onions");
    onions.addItemListener(p);
    this.add(onions);
    Checkbox sausage = new Checkbox("Sausage");
    sausage.addItemListener(p);
    this.add(sausage);
    Checkbox peppers = new Checkbox("Peppers");
    peppers.addItemListener(p);
    this.add(peppers);
    Checkbox extraCheese = new Checkbox("Extra Cheese");
    extraCheese.addItemListener(p);
    this.add(extraCheese);
    Checkbox ham = new Checkbox("Ham");
    ham.addItemListener(p);
    this.add(ham);
    Checkbox pineapple = new Checkbox("Pineapple");
    pineapple.addItemListener(p);
    this.add(pineapplec);
    Checkbox anchovies = new Checkbox("Anchovies");
    anchovies.addItemListener(p);
    this.add(anchovies);
 
    this.display = new TextField(String.valueOf(price));
    // so people can't change the price of the pizza
    display.setEditable(false); 
    this.add(display);
    
  }
  
  public void setPrice(double price) {
    this.price = price;
    display.setText(String.valueOf(price));
  }
  
  public double getPrice() {
    return this.price;
  }
  
}
 
class Pricer implements ItemListener {
 
  private Ingredients out;
 
  public Pricer(Ingredients out) {
    this.out = out;
  }
  
  public void itemStateChanged(ItemEvent ie) {
  
    double price = out.getPrice();
    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;
    else price -= 0.50;
    // Change the price
    out.setPrice(price);
  
  }
 
}

java.awt.CheckboxGroup
Checkbox groups are collections of checkboxes with the special property that
no more than one checkbox in the same group can be selected at a time. The
checkboxes in a CheckboxGroup
are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked
simultaneously. When the user checks one, all others are unchecked
automatically. 



The constructor for a CheckboxGroup
is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since
checkbox groups are themselves not user-interface widgets, just ways of
arranging checkboxes.



CheckboxGroup cbg = new
CheckboxGroup();



To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.



public Checkbox(String label,
CheckboxGroup cbg, boolean checked)



The label is the label for this Checkbox.
The CheckboxGroup is the
group you want this Checkbox
to belong to and must already exist.



At any time, you can get or set the selected Checkbox with these two methods:



  public Checkbox getSelectedCheckbox()
  public void setSelectedCheckbox(Checkbox box)




java.awt.CheckboxGroup example
The following program asks the customer how they're going to pay for their
pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may
want both anchovies and pineapple on their pizza, but they're unlikely to pay
with both Visa and American Express. 













import java.applet.*;    
import java.awt.*;
 
public class PaymentMethod extends Applet {
 
  public void init() {
    this.add(new Label("How will you pay for your pizza?"));
    CheckboxGroup cbg = new CheckboxGroup();
    this.add(new Checkbox("Visa", cbg, false));
    this.add(new Checkbox("Mastercard", cbg, false));
    this.add(new Checkbox("American Express", cbg, false));
    this.add(new Checkbox("Discover", cbg, false));
    this.add(new Checkbox("Cash", cbg, true)); // the default
  }
  
}
There isn't any action in this simple example applet. If you need to add
action as radio buttons are checked and unchecked, you do it just the same as
for any other Checkbox. 




java.awt.List
Scrolling lists are useful for storing long lists of things one to a line.
The things in the list are called items, but each one is just a String. For
example, 








List Methods
You create a new List
with one of these three constructors: 



  public List()
  public List(int numLines)
  public List(int numLines, boolean allowMultipleSelections)
For example, 



List l = new List(8, true);



numLines is the number of
items you want to be visible in the scrolling list. It is not necessarily the
same as the number of items in the list which is limited only by available
memory. allowMultipleSelections
says whether the user is allowed to select more than one item at once
(typically by Shift-clicking).



The following methods add items at the end of the list:



  public void add(String item)
  public void addItem(String item)
These two methods add items at the specified position in the list. 



  public void add(String item, int index)
  public void addItem(String item, int index)
The following methods remove items from the List: 



  public void removeAll()
  public void remove(String item)
  public void remove(int position)
  public void delItem(int position)

These methods allow you to retrive particular items from the
List: 
  public int getItemCount()
  public String getItem(int index)
  public String[] getItems()
You ran also replace a particular item: 



 public void replaceItem(String newValue, int index)
These methods allow you to determine which item the user has selected: 



  public int      getSelectedIndex()
  public int[]    getSelectedIndexes()
  public String   getSelectedItem()
  public String[] getSelectedItems()
  public Object[] getSelectedObjects()
If a list allows multiple selections, you should use the plural forms of the
above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). 



  public boolean isMultipleMode()
  public void    setMultipleMode(boolean b)
These methods allow you to manipulate the selection: 



  public void    select(int index)
  public void    deselect(int index)
  public boolean isIndexSelected(int index)
These two methods determine whether an item at a particular index is
currently visible in the List box:



  public int  getVisibleIndex()
  public void makeVisible(int index)




List Events
Lists can fire two separate types of events. When a list item is selected or
deselected, the List fires
an ItemEvent. However, when
the user double clicks on a list item, the List
fires an ActionEvent.
Therefore, you can register both an ItemListener
to process selections and/or an ActionListener
to process double clicks. 



public void addItemListener(ItemListener l)
public void removeItemListener(ItemListener l)
public void addActionListener(ActionListener l)
public void removeActionListener(ActionListener l)
The action command in the ActionEvent
is the list item which was double clicked. 




java.awt.Scrollbar
Lists, TextAreas, and ScrollPanes come with ready made
scrollbars. However if you want to scroll any other object you'll have to use a
java.awt.Scrollbar.
Scrollbars have many uses. At their most basic they're used for moving the
visible area. They can also be used to set a value between two numbers. Or they
can be used to flip through a number of screens as in a database operation that
looks at successive records. 



There are three constructors:



public Scrollbar()
public Scrollbar(int orientation)
public Scrollbar(int orientation, int value, int visible, int min, int max)
The orientation argument
is one of the mnemonic constants, Scrollbar.HORIZONTAL
or Scrollbar.VERTICAL. As
you expect this determines whether the Scrollbar
is laid out from left to right or top to bottom. 



A Scrollbar has an int value at all times. This value will
be between the minimum and
the maximum value set by the
last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.



Finally visible
represents the size of the visible portion of the scrollable area in pixels.
The Scrollbar uses this when
moving up or down a page.



A Scrollbar fires an
adjustment event when its value changes. You register an adjustment listener to
catch this event. This class needs an adjustmentValueChanged()
method with this signature:



public void
adjustmentValueChanged(AdjustmentEvent e)



The following program is an applet that changes the number in a TextField between 1 and 100 based on the
position of the thumb (the movable part of the Scrollbar). In a practical application the number would
of course mean something.







import java.applet.*;    
import java.awt.*;
import java.awt.event.*;
 
public class Scrollie extends Applet implements AdjustmentListener {
 
  private TextField t;
  private Scrollbar sb;
 
  public void init() {
    int initialValue = 1;
    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);
    sb.addAdjustmentListener(this);
    this.add(sb);
    this.t = new TextField(4);
    this.t.setText(String.valueOf(initialValue));    
    this.add(t);
  }
  
  public void adjustmentValueChanged(AdjustmentEvent e)
     
    int val = sb.getValue();
    this.t.setText(String.valueOf(val));
    
  }
  
}

Peer vs. Swing Components
I'm not going to talk much about Swing in this course, but most of what I
teach you about the standard AWT components carries over to their Swing
equivalents with only trivial changes. For example, here's yet another way to
write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold
and blue and with a yellow background. 



import java.awt.*;
import javax.swing.*;
 
 
public class SwingCubScout extends JApplet {
 
  public void init() {
  
     JLabel cubScouts = new JLabel("Cub Scouts!");
     cubScouts.setForeground(Color.blue);
     cubScouts.setBackground(Color.yellow);
     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 
     this.getContentPane().add(cubScouts);
     
  }
 
}
This is almost identical to the AWT-based Cub Scout applet, except that I've
imported the javax.swing
package and changed Label to
JLabel and Applet to JApplet. 




Week 6 Exercises

Write an applet that with a
     60 column by 10 row text area that allows the user to type some text. Add
     a button to this applet that clears the text area when it's pressed. 


Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.

Rewrite the payroll problem
     from week 2 as an applet. Provide a text field for the number of hours, a
     text field for the pay rate, and a non-editable text field for the output.
     Also provide labels to identify all three text fields and a button to
     calculate the result. 


Don't worry about minimum wage, number of hours in
the week, or other error conditions we checked before. In the event the user
enters data that cannot be interpreted as a number, don't put anything in the
output text field. In a couple of weeks, you'll learn how to bring up an error
dialog to handle these conditions.

Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.
We'll cover them next week




Getting into more fun Graphics



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class ShowColors2 extends JFrame {
   private JButton changeColorButton;
   private Color color = Color.LIGHT_GRAY;
   private Container container;
 
   // set up GUI
   public ShowColors2()
   {
      super( "Using JColorChooser" );
 
      container = getContentPane();
      container.setLayout( new FlowLayout() );
 
      // set up changeColorButton and register its event handler
      changeColorButton = new JButton( "Change Color" );
      changeColorButton.addActionListener(
 
         new ActionListener() {  // anonymous inner class
 
            // display JColorChooser when user clicks button
            public void actionPerformed( ActionEvent event )
            {
               color = JColorChooser.showDialog( 
                  ShowColors2.this, "Choose a color", color );
 
               // set default color, if no color is returned 
               if ( color == null )
                  color = Color.LIGHT_GRAY;
 
               // change content pane's background color
               container.setBackground( color );
            }
 
         } // end anonymous inner class
 
      ); // end call to addActionListener
 
      container.add( changeColorButton );
 
      setSize( 400, 130 );
      setVisible( true );
 
   } // end ShowColor2 constructor
 
   // execute application
   public static void main( String args[] )
   {
      ShowColors2 application = new ShowColors2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
}






import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class Shapes2 extends JFrame {
 
   // set window's title bar String, background color and dimensions
   public Shapes2()
   {
      super( "Drawing 2D Shapes" );
 
      getContentPane().setBackground( Color.WHITE );
      setSize( 400, 400 );
      setVisible( true );
   }
 
   // draw general paths
   public void paint( Graphics g )
   {
      super.paint( g );  // call superclass's paint method
 
      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };
      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };
 
      Graphics2D g2d = ( Graphics2D ) g;
      GeneralPath star = new GeneralPath();  // create GeneralPath object
 
      // set the initial coordinate of the General Path
      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );
 
      // create the star--this does not draw the star
      for ( int count = 1; count < xPoints.length; count++ )
         star.lineTo( xPoints[ count ], yPoints[ count ] );
 
      star.closePath();  // close the shape
 
      g2d.translate( 200, 200 );  // translate the origin to (200, 200)
 
      // rotate around origin and draw stars in random colors
      for ( int count = 1; count <= 20; count++ ) {
         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system
 
         // set random drawing color
         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),
            ( int ) ( Math.random() * 256 ),              
            ( int ) ( Math.random() * 256 ) ) );
 
         g2d.fill( star );  // draw filled star
      }
 
   } // end method paint
 
   // execute application
   public static void main( String args[] )
   {
      Shapes2 application = new Shapes2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
  
} 

An example of text fields in Java
The following applet reads text from one TextField
and capitalizes it in another TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction(input, output);
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
}
 
 
class CapitalizerAction implements ActionListener {
 
  private TextField in;
  private TextField out;
 
  public CapitalizerAction(TextField in, TextField out) {
    this.in = in;
    this.out = out;
  }
 
  public void actionPerformed(ActionEvent ae) {
 
    String s = in.getText();
    out.setText(s.toUpperCase());
 
  }
 
}
In this program, a different pattern is used for handling events. The
constructor for the CapitalizerAction
class is used to pass in references to the different components the actionPerformed() method affects. 




An example of text fields in Java
An alternate pattern uses an inner class so the private fields can be
accessed directly.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class CapitalizeApplet extends Applet {
 
  private TextField input;
  private TextField output;
  
  public void init () {
   
     // Construct the TextFields
     this.input = new TextField(40);
     this.output = new TextField(40);
     this.output.setEditable(false);
     Button b = new Button("Capitalize");
 
     // add the button to the layout
     this.add(input);
     this.add(b);
     this.add(output);
 
     // specify that action events sent by the
     // button or the input TextField should be handled 
     // by the same CapitalizerAction object
     CapitalizerAction ca = new CapitalizerAction();
     b.addActionListener(ca);
     this.input.addActionListener(ca);
 
     // notice that ActionEvents produced by output are ignored.
   
   }
 
  class CapitalizerAction implements ActionListener {
 
    public void actionPerformed(ActionEvent ae) {
 
      String s = input.getText();
      output.setText(s.toUpperCase());
 
    }
 
  }
 
 
}

TextArea
The java.awt.TextArea
class is a subclass of java.awt.TextComponent
that provides a widget for editing multiple lines of text. It's useful for
input and output.







There are five constructors:



  public TextArea()
  public TextArea(String text)
  public TextArea(int rows, int columns)
  public TextArea(String text, int rows, int columns)
  public TextArea(String text, int rows, int columns, int scrollbars)
Because of the way Java lays out components, you should not use the noargs
constructor. Either start off with a String
or specify the number of rows and columns this area is expected to hold. For
example, 



TextArea address = new TextArea("Type your address here", 5, 80);
By default, TextAreas don't have scrollbars. However you can add them by
passing one of these constants to the constructor: 



TextArea.SCROLLBARS_BOTH 
TextArea.SCROLLBARS_HORIZONTAL_ONLY 
TextArea.SCROLLBARS_NONE 
TextArea.SCROLLBARS_VERTICAL_ONLY
For example, 



TextArea instructions = 
 new TextArea("", 15, 70, TextArea.SCROLLBARS_VERTICAL_ONLY);
Unlike text fields, text areas do not generate action events when the user
hits return inside the area. Instead, the line is broken and the caret moves on
to the next row. 



However, the getText()
method does return the contents of the TextArea,
and the setText() method
does change it. The setEditable()
method lets you determine whether or not, the user can modify the contents of a
TextField. If these methods
sound familiar it's because they're both inherited from the common superclass
of TextField and TextArea, TextComponent.



Furthermore, you can append text to a TextArea
with the append() method,
insert text into the middle of a TextArea
with the insert() method,
and replace a block of text with the replaceRange()
method:



public void insert(String text, int position)
public void append(String text)  
public void replaceRange(String text, int start, int end)




TextComponent
Both TextArea and TextField are subclasses of java.awt.TextComponent. This class
contains methods common to both classes including several you've already seen: getText(), setText(), and setEditable().
The TextComponent class also
defines methods for manipulating the selection and the caret and for processing
TextEvents. 



The selection is used for copy and paste and other purposes. The first
character in a TextComponent
is character 0; the second is character 1, and so on.



  public int    getSelectionStart()
  public void   setSelectionStart(int selectionStart)
  public int    getSelectionEnd()
  public void   setSelectionEnd(int selectionEnd)
  public void   select(int selectionStart, int selectionEnd)
  public void   selectAll()
  public String getSelectedText()
The caret is the insertion point. It's where text appears when the user
types. There are two methods to adjust it: 



  public void setCaretPosition(int position)
  public int  getCaretPosition()

TextEvents
Both TextArea and TextField can install a TextListener that catches TextEvents. TextComponents fire TextEvents every time the text of the
component changes. This is more or less every time the user hits a key in the
component. 



The java.awt.event.TextListener
interface defines a single method, textValueChanged():



public void textValueChanged(TextEvent te)
You register a TextListener
with a TextComponent by
calling the component's addTextListener()
method. For example, 



TextArea password = new TextArea(24)
password.addTextListener(new PasswordChecker());
However, most of the time it's sufficient to just get and set the text as
you need it. It's really quite rare that you need to process it character by
character. 



A TextListener can be
removed by calling removeTextListener().



public void
removeTextListener(TextListener tl)




java.awt.Canvas
The java.awt.Canvas class
is a rectangular area on which you can draw using the methods of java.awt.Graphics discussed last week.
The Canvas class has only
three methods: 



  public Canvas()
  public void addNotify()
  public void paint(Graphics g)
You generally won't instantiate a canvas directly. Instead you'll subclass
it and override the paint()
method in your subclass to draw the picture you want. 



For example the following Canvas
draws a big red oval you can add to your applet.



import java.awt.*;
 
public class RedOval extends Canvas {
 
  public void paint(Graphics g) {
  
    Dimension d = this.getSize();
    g.setColor(Color.red);
    g.fillOval(0, 0, d.width, d.height);
      
  }
  
  public Dimension getMinimumSize() {
    return new Dimension(50, 100);  
  }
 
  public Dimension getPreferredSize() {
    return new Dimension(150, 300);  
  }
 
  public Dimension getMaximumSize() {
    return new Dimension(200, 400);  
  }
 
}
Any applet that uses components should not also override paint(). Doing so will have unexpected
effects because of the way Java arranges components. Instead, create a Canvas object and do your drawing in its
paint() method.



Custom canvases are added to applets just like any other component. For
example,



  public void init() {
    this.add(new RedOval());
  }
Canvases themselves do not normally fire any events. Next week, we'll see
how to change that in the subclasses. 




An alternate approach
import java.awt.*;
 
 
public class ColoredOval extends Canvas {
 
  public ColoredOval() {
    this(Color.RED, 100, 100);
  }
 
  public ColoredOval(Color c) {
    this(c, 100, 100);
  }
 
  public ColoredOval(int width, int height) {
    this(Color.RED, width, height);
  }
 
  public ColoredOval(Color c, int width, int height) {
    this.setColor(c);
    this.setSize(width, height);
  }
 
  public void paint(Graphics g) {  
    Dimension d = this.getSize();
    g.fillOval(0, 0, d.width, d.height);
  }
 
}
This is almost but not quite the same effect as the previous applet. (It's a
little less resizeable.) 




java.awt.Choice
The java.awt.Choice class
implements a popup menu with a fixed position. (The java.awt.PopupMenu class is a popup menu
with no fixed position. It pops up when the user clicks 




and holds the right mouse button.) 




Creating a choice menu is a little more complex than creating the other user
interface components you've seen. There's an extra step, adding the menu items
to the menu. That is the five steps are




Declare the Choice 
Allocate the Choice 
Add the menu items to the Choice 
Add the Choice to the layout 
Add an ItemListener to the Choice 

For example 



 public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    add(ch);
 
  }   

Methods of java.awt.Choice
The Choice class has a
number of methods to add, remove, and return different items from the list. The
list starts counting at 0. 



  public int    getItemCount()
  public String getItem(int index)
  public void   add(String item)
  public void   addItem(String item)
  public void   insert(String item, int position)
  public void   remove(String item)
  public void   remove(int position)
  public void   removeAll()
However, most of the item you'll just build the Choice when the applet starts up, and
not modify it later. 



These methods get or set the current selected item in the Choice, that is the item that's shown.



  public void     removeAll()
  public String   getSelectedItem()
  public Object[] getSelectedObjects()
  public int      getSelectedIndex()
  public void     select(int position)
  public void     select(String item)




ItemListeners
When the user changes the selected item in a Choice, the Choice
fires two ItemListener
events, one to indicate that the original selection has been deselected and the
other to indicate that a new selection has been made. You can process these
events by registering an ItemListener
object with your Choice. 



You do not always need to do this. It is not uncommon to only check the
value of a Choice when some
other event occurs like a Button
press.



For example, the following applet builds a Choice menu with the numbers from 1 to 5. When the user
makes a selection, the applet beeps that many times.



import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class MultiBeep extends Applet {
  
  public void init() {
 
    Choice ch;
    ch = new Choice();
    ch.addItem("1");
    ch.addItem("2");
    ch.addItem("3");
    ch.addItem("4");
    ch.addItem("5");
    this.add(ch);
    ch.addItemListener(new BeepItem());
 
  }    
 
}
 
 
class BeepItem implements ItemListener {
 
  public void itemStateChanged(ItemEvent ie) {
 
    if (ie.getStateChange() == ItemEvent.SELECTED) {
      String name = (String) ie.getItem();
      Toolkit tk = Toolkit.getDefaultToolkit();
      try {
        int n = Integer.parseInt(name);
        for (int i = 0; i < n; i++) tk.beep();
      }
      catch (Exception e) {
        tk.beep();
      }
    }
 
  }
 
}

The BeepItem
class implements the ItemListener
interface. It filters out events caused by items being deselected with ItemEvent.getStateChange() and only
beeps if an item was selected. The available convenience constants you can
check are: 
ItemEvent.DESELECTED 
ItemEvent.ITEM_FIRST 
ItemEvent.ITEM_LAST 
ItemEvent.ITEM_STATE_CHANGED 
ItemEvent.SELECTED

The ItemEvent.getItem()
method is used to retrieve the actual selected item.




java.awt.Checkbox
Check boxes are used to select a boolean
value. Each Checkbox has a
label that should be used to tell the user what the Checkbox represents. For instance a Checkbox with the label
"Anchovies" would be checked if the user wants anchovies on their
pizza and unchecked if they don't. 







Checkboxes are often used to select from a list of possible choices when as
few selections as zero or as many as everything on the list may be made. Adding
a Checkbox to an applet is
simple. Just declare it, construct it and add it.



  Checkbox c c = new Checkbox("Pepperoni"));
  add(c);
As usual these steps may be combined into the single line 



add(new
Checkbox("Pepperoni"));



By default check boxes are unchecked when created. If you want a Checkbox to start life checked, use the
following constructor instead:



add(new Checkbox("Pepperoni",
null, true));



The null is a reference
to a CheckboxGroup. Passing null for this argument says that this Checkbox does not belong to a CheckboxGroup.



Every Checkbox has a boolean value, either true or false. When the Checkbox
is checked that value is true.
When it is unchecked that value is false. You access this value using the Checkbox's getState() and setState(boolean
b) methods. For example



  private void handleCheckbox(Checkbox c) {
  
    if (c.getState()) price += 0.50;
    else price -= 0.50;
  
  }

Checkbox Events
When the a Checkbox
changes state, normally as a result of user action, it fires an ItemEvent. Most of the time you ignore
this event. Instead you manually check the state of a Checkbox when you need to know it.
However if you want to know immediately when a Checkbox changes state, you can register an ItemListener for the Checkbox. 



An ItemEvent is exactly
the same as the item event fired by a Choice.
In fact item events are used to indicate selections or deselections in any sort
of list including checkboxes, radio buttons, choices, and lists.



For example, the following program is an applet that asks the age-old
question, "What do you want on your pizza?" When an ingredient is
checked the price of the pizza goes up by fifty cents. When an ingredient is
unchecked fifty cents is taken off. The price is shown in a TextField.













import java.applet.*;
import java.awt.*;
import java.awt.event.*;
 
public class Ingredients extends Applet {
 
  private TextField display;
  private double price = 7.00;
 
  public void init() {
  
    this.add(new Label("What do you want on your pizza?", Label.CENTER));
      
    Pricer p = new Pricer(this);
    Checkbox pepperoni = new Checkbox("Pepperoni");
    this.add(pepperoni);
    pepperoni.addItemListener(p);
    Checkbox olives = new Checkbox("Olives");
    olives.addItemListener(p);
    this.add(olives);
    Checkbox onions = new Checkbox("Onions");
    onions.addItemListener(p);
    this.add(onions);
    Checkbox sausage = new Checkbox("Sausage");
    sausage.addItemListener(p);
    this.add(sausage);
    Checkbox peppers = new Checkbox("Peppers");
    peppers.addItemListener(p);
    this.add(peppers);
    Checkbox extraCheese = new Checkbox("Extra Cheese");
    extraCheese.addItemListener(p);
    this.add(extraCheese);
    Checkbox ham = new Checkbox("Ham");
    ham.addItemListener(p);
    this.add(ham);
    Checkbox pineapple = new Checkbox("Pineapple");
    pineapple.addItemListener(p);
    this.add(pineapplec);
    Checkbox anchovies = new Checkbox("Anchovies");
    anchovies.addItemListener(p);
    this.add(anchovies);
 
    this.display = new TextField(String.valueOf(price));
    // so people can't change the price of the pizza
    display.setEditable(false); 
    this.add(display);
    
  }
  
  public void setPrice(double price) {
    this.price = price;
    display.setText(String.valueOf(price));
  }
  
  public double getPrice() {
    return this.price;
  }
  
}
 
class Pricer implements ItemListener {
 
  private Ingredients out;
 
  public Pricer(Ingredients out) {
    this.out = out;
  }
  
  public void itemStateChanged(ItemEvent ie) {
  
    double price = out.getPrice();
    if (ie.getStateChange() == ItemEvent.SELECTED) price += 0.50;
    else price -= 0.50;
    // Change the price
    out.setPrice(price);
  
  }
 
}

java.awt.CheckboxGroup
Checkbox groups are collections of checkboxes with the special property that
no more than one checkbox in the same group can be selected at a time. The
checkboxes in a CheckboxGroup
are often called radio buttons. Checkboxes that are members of the same CheckboxGroup cannot be checked
simultaneously. When the user checks one, all others are unchecked
automatically. 



The constructor for a CheckboxGroup
is trivial. No arguments are needed. You do not even need to add the CheckboxGroup to the applet since
checkbox groups are themselves not user-interface widgets, just ways of
arranging checkboxes.



CheckboxGroup cbg = new
CheckboxGroup();



To make check boxes act like radio buttons, use this constructor for each Checkbox in the group.



public Checkbox(String label,
CheckboxGroup cbg, boolean checked)



The label is the label for this Checkbox.
The CheckboxGroup is the
group you want this Checkbox
to belong to and must already exist.



At any time, you can get or set the selected Checkbox with these two methods:



  public Checkbox getSelectedCheckbox()
  public void setSelectedCheckbox(Checkbox box)




java.awt.CheckboxGroup example
The following program asks the customer how they're going to pay for their
pizza, Visa, Mastercard, American Express, Discover, cash or check. Someone may
want both anchovies and pineapple on their pizza, but they're unlikely to pay
with both Visa and American Express. 













import java.applet.*;    
import java.awt.*;
 
public class PaymentMethod extends Applet {
 
  public void init() {
    this.add(new Label("How will you pay for your pizza?"));
    CheckboxGroup cbg = new CheckboxGroup();
    this.add(new Checkbox("Visa", cbg, false));
    this.add(new Checkbox("Mastercard", cbg, false));
    this.add(new Checkbox("American Express", cbg, false));
    this.add(new Checkbox("Discover", cbg, false));
    this.add(new Checkbox("Cash", cbg, true)); // the default
  }
  
}
There isn't any action in this simple example applet. If you need to add
action as radio buttons are checked and unchecked, you do it just the same as
for any other Checkbox. 




java.awt.List
Scrolling lists are useful for storing long lists of things one to a line.
The things in the list are called items, but each one is just a String. For
example, 








List Methods
You create a new List
with one of these three constructors: 



  public List()
  public List(int numLines)
  public List(int numLines, boolean allowMultipleSelections)
For example, 



List l = new List(8, true);



numLines is the number of
items you want to be visible in the scrolling list. It is not necessarily the
same as the number of items in the list which is limited only by available
memory. allowMultipleSelections
says whether the user is allowed to select more than one item at once
(typically by Shift-clicking).



The following methods add items at the end of the list:



  public void add(String item)
  public void addItem(String item)
These two methods add items at the specified position in the list. 



  public void add(String item, int index)
  public void addItem(String item, int index)
The following methods remove items from the List: 



  public void removeAll()
  public void remove(String item)
  public void remove(int position)
  public void delItem(int position)

These methods allow you to retrive particular items from the
List: 
  public int getItemCount()
  public String getItem(int index)
  public String[] getItems()
You ran also replace a particular item: 



 public void replaceItem(String newValue, int index)
These methods allow you to determine which item the user has selected: 



  public int      getSelectedIndex()
  public int[]    getSelectedIndexes()
  public String   getSelectedItem()
  public String[] getSelectedItems()
  public Object[] getSelectedObjects()
If a list allows multiple selections, you should use the plural forms of the
above methods. You can determine whether multiple selections are allowed with isMultipleMode() and change it with setMultipleMode(). 



  public boolean isMultipleMode()
  public void    setMultipleMode(boolean b)
These methods allow you to manipulate the selection: 



  public void    select(int index)
  public void    deselect(int index)
  public boolean isIndexSelected(int index)
These two methods determine whether an item at a particular index is
currently visible in the List box:



  public int  getVisibleIndex()
  public void makeVisible(int index)




List Events
Lists can fire two separate types of events. When a list item is selected or
deselected, the List fires
an ItemEvent. However, when
the user double clicks on a list item, the List
fires an ActionEvent.
Therefore, you can register both an ItemListener
to process selections and/or an ActionListener
to process double clicks. 



public void addItemListener(ItemListener l)
public void removeItemListener(ItemListener l)
public void addActionListener(ActionListener l)
public void removeActionListener(ActionListener l)
The action command in the ActionEvent
is the list item which was double clicked. 




java.awt.Scrollbar
Lists, TextAreas, and ScrollPanes come with ready made
scrollbars. However if you want to scroll any other object you'll have to use a
java.awt.Scrollbar.
Scrollbars have many uses. At their most basic they're used for moving the
visible area. They can also be used to set a value between two numbers. Or they
can be used to flip through a number of screens as in a database operation that
looks at successive records. 



There are three constructors:



public Scrollbar()
public Scrollbar(int orientation)
public Scrollbar(int orientation, int value, int visible, int min, int max)
The orientation argument
is one of the mnemonic constants, Scrollbar.HORIZONTAL
or Scrollbar.VERTICAL. As
you expect this determines whether the Scrollbar
is laid out from left to right or top to bottom. 



A Scrollbar has an int value at all times. This value will
be between the minimum and
the maximum value set by the
last two arguments to the constructor. When a Scrollbar is created, its value is given by the value argument. The default is 0.



Finally visible
represents the size of the visible portion of the scrollable area in pixels.
The Scrollbar uses this when
moving up or down a page.



A Scrollbar fires an
adjustment event when its value changes. You register an adjustment listener to
catch this event. This class needs an adjustmentValueChanged()
method with this signature:



public void
adjustmentValueChanged(AdjustmentEvent e)



The following program is an applet that changes the number in a TextField between 1 and 100 based on the
position of the thumb (the movable part of the Scrollbar). In a practical application the number would
of course mean something.







import java.applet.*;    
import java.awt.*;
import java.awt.event.*;
 
public class Scrollie extends Applet implements AdjustmentListener {
 
  private TextField t;
  private Scrollbar sb;
 
  public void init() {
    int initialValue = 1;
    sb = new  Scrollbar(Scrollbar.HORIZONTAL, initialValue, 100, 1, 100);
    sb.addAdjustmentListener(this);
    this.add(sb);
    this.t = new TextField(4);
    this.t.setText(String.valueOf(initialValue));    
    this.add(t);
  }
  
  public void adjustmentValueChanged(AdjustmentEvent e)
     
    int val = sb.getValue();
    this.t.setText(String.valueOf(val));
    
  }
  
}

Peer vs. Swing Components
I'm not going to talk much about Swing in this course, but most of what I
teach you about the standard AWT components carries over to their Swing
equivalents with only trivial changes. For example, here's yet another way to
write an applet that says "Cub Scouts!" in 24 point, SansSerif, bold
and blue and with a yellow background. 



import java.awt.*;
import javax.swing.*;
 
 
public class SwingCubScout extends JApplet {
 
  public void init() {
  
     JLabel cubScouts = new JLabel("Cub Scouts!");
     cubScouts.setForeground(Color.blue);
     cubScouts.setBackground(Color.yellow);
     cubScouts.setFont(new Font("Sans", Font.BOLD, 24)); 
     this.getContentPane().add(cubScouts);
     
  }
 
}
This is almost identical to the AWT-based Cub Scout applet, except that I've
imported the javax.swing
package and changed Label to
JLabel and Applet to JApplet. 




Week 6 Exercises

Write an applet that with a
     60 column by 10 row text area that allows the user to type some text. Add
     a button to this applet that clears the text area when it's pressed. 


Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.

Rewrite the payroll problem
     from week 2 as an applet. Provide a text field for the number of hours, a
     text field for the pay rate, and a non-editable text field for the output.
     Also provide labels to identify all three text fields and a button to
     calculate the result. 


Don't worry about minimum wage, number of hours in
the week, or other error conditions we checked before. In the event the user
enters data that cannot be interpreted as a number, don't put anything in the
output text field. In a couple of weeks, you'll learn how to bring up an error
dialog to handle these conditions.

Don't worry excessively about making the applet
look good. Before you can do that you'll need to learn about layout managers.
We'll cover them next week




Getting into more fun Graphics



import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class ShowColors2 extends JFrame {
   private JButton changeColorButton;
   private Color color = Color.LIGHT_GRAY;
   private Container container;
 
   // set up GUI
   public ShowColors2()
   {
      super( "Using JColorChooser" );
 
      container = getContentPane();
      container.setLayout( new FlowLayout() );
 
      // set up changeColorButton and register its event handler
      changeColorButton = new JButton( "Change Color" );
      changeColorButton.addActionListener(
 
         new ActionListener() {  // anonymous inner class
 
            // display JColorChooser when user clicks button
            public void actionPerformed( ActionEvent event )
            {
               color = JColorChooser.showDialog( 
                  ShowColors2.this, "Choose a color", color );
 
               // set default color, if no color is returned 
               if ( color == null )
                  color = Color.LIGHT_GRAY;
 
               // change content pane's background color
               container.setBackground( color );
            }
 
         } // end anonymous inner class
 
      ); // end call to addActionListener
 
      container.add( changeColorButton );
 
      setSize( 400, 130 );
      setVisible( true );
 
   } // end ShowColor2 constructor
 
   // execute application
   public static void main( String args[] )
   {
      ShowColors2 application = new ShowColors2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
 
}






import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class Shapes2 extends JFrame {
 
   // set window's title bar String, background color and dimensions
   public Shapes2()
   {
      super( "Drawing 2D Shapes" );
 
      getContentPane().setBackground( Color.WHITE );
      setSize( 400, 400 );
      setVisible( true );
   }
 
   // draw general paths
   public void paint( Graphics g )
   {
      super.paint( g );  // call superclass's paint method
 
      int xPoints[] = { 55, 67, 109, 73, 83, 55, 27, 37, 1, 43 };
      int yPoints[] = { 0, 36, 36, 54, 96, 72, 96, 54, 36, 36 };
 
      Graphics2D g2d = ( Graphics2D ) g;
      GeneralPath star = new GeneralPath();  // create GeneralPath object
 
      // set the initial coordinate of the General Path
      star.moveTo( xPoints[ 0 ], yPoints[ 0 ] );
 
      // create the star--this does not draw the star
      for ( int count = 1; count < xPoints.length; count++ )
         star.lineTo( xPoints[ count ], yPoints[ count ] );
 
      star.closePath();  // close the shape
 
      g2d.translate( 200, 200 );  // translate the origin to (200, 200)
 
      // rotate around origin and draw stars in random colors
      for ( int count = 1; count <= 20; count++ ) {
         g2d.rotate( Math.PI / 10.0 );  // rotate coordinate system
 
         // set random drawing color
         g2d.setColor( new Color( ( int ) ( Math.random() * 256 ),
            ( int ) ( Math.random() * 256 ),              
            ( int ) ( Math.random() * 256 ) ) );
 
         g2d.fill( star );  // draw filled star
      }
 
   } // end method paint
 
   // execute application
   public static void main( String args[] )
   {
      Shapes2 application = new Shapes2();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }
  
}