Interfaces and Polymorphism - Java Concepts - page 563

listener.actionPerformed(event);

As a result, the message is printed.

You can think of the actionPerformed method as another example of a callback,
similar to the measure method of the Measurer class. The windowing toolkit calls
the actionPerformed method whenever the button is pressed, whereas the
DataSet calls the measure method whenever it needs to measure an object.

You can test this program out by opening a console window, starting the
ButtonViewer program from that console window, clicking the button, and
watching the messages in the console window (see Figure 3 ).

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Figure 3

Implementing an Action Listener

ch09/button1/ButtonViewer.java

1 import java.awt.event.ActionListener;
2 import javax.swing.JButton;
3 import javax.swing.JFrame;
4
5 /**
6 This program demonstrates how to install an action listener.
7 */
8 public class ButtonViewer
9 {
10 public static void main(String[] args)