GUI COMPONENTS - Introduction to Java Programming - page 640

17.1 Introduction
Swing provides many GUI components for developing a comprehensive user interface.

Key
Point

Previous chapters briefly introduced JButton , JCheckBox , JRadioButton , JLabel ,
JTextField , and JPasswordField . This chapter introduces in detail how the events are
processed for these components. We will also introduce JTextArea , JComboBox , JList ,
JScrollBar , and JSlider . More GUI components such as JMenu , JToolBar ,
JTabbedPane , JSplitPane , JSpinner , JTree , and JTable will be introduced in bonus
Web Chapters 36-40.

17.2 Events for JCheckBox , JRadioButton , and
JTextField
A GUI component may fire many types of events. ActionEvent is commonly
processed for JCheckBox , JRadioButton , and JTextField , and ItemEvent can
be used for JCheckBox and JRadioButton .
In the previous chapter, you learned how to handle an action event for JButton . This section
introduces handling events for check boxes, radio buttons, and text fields.
When a JCheckBox or a JRadioButton is clicked (that is, checked or unchecked), it
fires an ItemEvent and then an ActionEvent . When you press the Enter key on a
JTextField , it fires an ActionEvent .
Listing 17.1 gives a program that demonstrates how to handle events from check boxes,
radio buttons, and text fields. The program displays a label and allows the user to set the col-
ors of the text in the label using radio buttons, set fonts using check boxes, and set new text
entered from a text field, as shown in Figure 17.1.

Key
Point

JPanel with
BorderLayout for
a label and a text field

F IGURE 17.1

The program demonstrates check boxes, radio buttons, and text fields.

L ISTING 17.1 GUIEventDemo.java
1 import java.awt.*;
2 import java.awt.event.*;
3 import javax.swing.*;
4 import javax.swing.border.*;
5
6 public class GUIEventDemo extends JFrame {
7 private JLabel jlblMessage = new JLabel( "Hello" , JLabel.CENTER); create label

8
9

// Create check boxes to set the font for the message

10 private JCheckBox jchkBold = new JCheckBox( "Bold" );

create check boxes

11 private JCheckBox jchkItalic = new JCheckBox( "Italic" );

12
13

// Create three radio buttons to set message colors

14 private JRadioButton jrbRed = new JRadioButton( "Red" );

create radio buttons

15 private JRadioButton jrbGreen = new JRadioButton( "Green" );

16 private JRadioButton jrbBlue = new JRadioButton( "Blue" );

17
18 // Create a text field for setting a new message