Swing Hacks

Fire Events and Stay Bug Free #94

Chapter 12, Miscellany

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473

HACK

The Problem

To illustrate the problem and its various solutions, consider the listener class

in Example 12-11.

This listener hangs on to a

String and prints that string to standard out

when

handleEvent( ) is called. Also, if the string is a specific value—C in this

case—it removes itself from the event source. If you can see why that’s going

to be a big deal, congratulations. If not, read on.

Next, define an abstract class to exercise various means of firing the event.

This is shown in Example 12-12.

This abstract class requires subclasses to include

addListener( ),

removeListener( ), and fireEvent( ) methods. It also implements a test

method that creates five listeners, identified as the letters

A through E, and

fires an event to each one.

Example 12-11. A simple event listener

import java.util.*;

public class TestEventListener extends Object

implements EventListener {

String id;

public TestEventListener (String id) {

this.id = id;

}

public void handleEvent (EventObject o) {

System.out.println (id + " called");

if (id.equals ("C")) {

((TestEventSource) o.getSource( )).removeListener (this);

}

}

}

Example 12-12. Abstract class for testing event-firing techniques

public abstract class TestEventSource {

public abstract void addListener (TestEventListener l);

public abstract void removeListener (TestEventListener l);

public abstract void fireEvent ...