GUI Components: Part 1 - Java: How to Program Early Objects - page 499

are mutually exclusive —only one in the group can be selected at any time, just like the but-
tons on a car radio. We first discuss class JCheckBox .

12.10.1 JCheckBox
The application of Figs. 12.17-12.18 uses two JCheckBox es to select the desired font style
of the text displayed in a JTextField . When selected, one applies a bold style and the other
an italic style. If both are selected, the style is bold and italic. When the application initially
executes, neither JCheckBox is checked (i.e., they're both false ), so the font is plain. Class
CheckBoxTest (Fig. 12.18) contains the main method that executes this application.

1 // Fig. 12.17: CheckBoxFrame.java

2 // JCheckBoxes and item events.

3 import java.awt.FlowLayout;

4 import java.awt.Font;

5 import java.awt.event.ItemListener;

6 import java.awt.event.ItemEvent;

7 import javax.swing.JFrame;

8 import javax.swing.JTextField;

9 import javax.swing.JCheckBox;

10
11

public class CheckBoxFrame extends JFrame

12

{

13

private final JTextField textField; // displays text in changing fonts

14 private final JCheckBox boldJCheckBox; // to select/deselect bold

private final JCheckBox italicJCheckBox; // to select/deselect italic 15

16
17 // CheckBoxFrame constructor adds JCheckBoxes to JFrame

18 public CheckBoxFrame()

19 {

20 super ( "JCheckBox Test" );

21 setLayout( new FlowLayout());

22
23 // set up JTextField and set its font

24 textField = new JTextField( "Watch the font style change" , 20 );

25 textField.setFont( new Font( "Serif" , Font.PLAIN , 14 ));

26 add(textField); // add textField to JFrame

27
28 boldJCheckBox = new JCheckBox( "Bold" );

29 italicJCheckBox = new JCheckBox( "Italic" );

30 add(boldJCheckBox); // add bold checkbox to JFrame

31 add(italicJCheckBox); // add italic checkbox to JFrame

32
33 // register listeners for JCheckBoxes

CheckBoxHandler handler = new CheckBoxHandler();
boldJCheckBox.addItemListener(handler);
italicJCheckBox.addItemListener(handler);

34

35

36

37 }

38
39 // private inner class for ItemListener event handling

40 private class CheckBoxHandler implements ItemListener

41 {

Fig. 12.17 | JCheckBox es and item events. (Part 1 of 2.)