EVENT-DRIVEN PROGRAMMING - Introduction to Java Programming - page 601

The ActionListener interface contains the actionPerformed method for processing the
event. Your listener class must override this method to respond to the event. Listing 16.1 gives
the code that processes the ActionEvent on the two buttons. When you click the OK button,
the message “OK button clicked” is displayed. When you click the Cancel button, the mes-
sage “Cancel button clicked” is displayed, as shown in Figure 16.2.

L ISTING 16.1 HandleEvent.java
1 import javax.swing.*;
2 import java.awt.event.*;
3
4 public class

HandleEvent extends JFrame {

5 public HandleEvent() {
6 // Create two buttons
7 JButton jbtOK = new JButton( "OK" );
8 JButton jbtCancel = new JButton( "Cancel" );
9
10 // Create a panel to hold buttons
11 JPanel panel = new JPanel();
12 panel.add(jbtOK);
13 panel.add(jbtCancel);
14
15 add(panel); // Add panel to the frame
16
17

// Register listeners

18
19 CancelListenerClass listener2 = new CancelListenerClass();
20
21 jbtCancel.addActionListener(listener2);
22 }
23
24

OKListenerClass listener1 = new OKListenerClass(); create listener

jbtOK.addActionListener(listener1);

register listener

public static void main(String[] args) {

25
26 frame.setTitle( "Handle Event" );
27 frame.setSize( 200 , 150 );
28 frame.setLocation( 200 , 100 );
29 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
30 frame.setVisible( true );
31 }
32 }
33
34 class

JFrame frame = new HandleEvent();

OKListenerClass implements ActionListener {

listener class

35 @Override
36 public void actionPerformed(ActionEvent e) {
37 System.out.println ( "OK button clicked" );
38 }
39 }
40
41 class

process event

CancelListenerClass implements ActionListener { listener class

42 @Override
43 public void actionPerformed(ActionEvent e) {
44 System.out.println( "Cancel button clicked" );
45 }
46 }

process event

Two listener classes are defined in lines 34-46. Each listener class implements
ActionListener to process ActionEvent . The object listener1 is an instance of
OKListenerClass (line 18), which is registered with the button jbtOK (line 20). When the
OK

button is clicked, the actionPerformed(ActionEvent) method (line 36) in