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<TITLE>Writing Advanced Applications, Chapter 7: AWT Debugging</TITLE>
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<H2>Writing Advanced Applications<BR>
<FONT SIZE="3">Chapter 7 Continued: Abstract Window Toolkit Debugging</FONT></H2>
<FONT SIZE="-1">[<A HREF="servlet.html"><<BACK</A>] [<A HREF="index.html#contents">CONTENTS</A>] [<A HREF="stack.html">NEXT>></A>]</FONT></DIV>
<P>
Before the new Abstract Window Toolkit (AWT) Event mechanism introduced
in JDK 1.1, events were received by a component such as a <CODE>TextField</CODE>,
and propagated upwards to its parent components. This meant you could
simply add some diagnostic code to the component's
<CODE>handleEvent</CODE> or <CODE>action</CODE> method to monitor
the events as they arrived.
<P>
With the introduction of JDK 1.1 and the new system event queue, events are
delivered to an event queue instead of the component itself. The events
are then dispatched from the System Event queue to event listeners that
register to be notified when an event has been dispatched for that object.
<HR>
<H3>Using AWTEventListener</H3>
You can use an <CODE>AWTEventListener</CODE> to monitor the AWT events from a
system event queue. This listener takes an event mask built from
an <CODE>OR</CODE> operation of the <CODE>AWTEvent</CODE>s you want to monitor.
To obtain a simple list of the <CODE>AWTEvent</CODE> events, use the
<CODE>javap -public java.awt.AWTEvent</CODE> command. This example tracks
the mouse and focus events.
<BLOCKQUOTE>
<HR>
<STRONG>Note:</STRONG><BR>
It is advised to not use <CODE>AWTEventListener</CODE> in a
shipping product as it will degrade system performance
<HR>
</BLOCKQUOTE>
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<PRE>
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//EventTest.java
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class EventTest extends JFrame {
public EventTest() {
JButton jb1=new JButton("hello");
getContentPane().add(jb1);
//AWTEventListener
getToolkit().addAWTEventListener(
new AWTEventListener() {
public void eventDispatched(AWTEvent e) {
System.out.println(e+"\n");
}
}, AWTEvent.MOUSE_EVENT_MASK |
AWTEvent.FOCUS_EVENT_MASK
);
}
public static void main (String args[]) {
EventTest et=new EventTest();
et.setSize(300,300);
et.pack();
et.show();
}
}
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[ This page was updated: <!-- new date --> 13-Oct-99 ]</font></P>
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