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Tags/Keywords : Event-handling-and-Java-Technology - Event-handling-and-Java-Technology - Coding-Tips-on-Java Example
Author : Amit
Date (Year/Month/Date): 2009-01-25
Event handling and Java Technology based solution and Ideas

Please be informed that NONE of the design/code from this
page is claiming to be some sort of best practices and we DO NOT expect
any of our visitor/reader of this page to assume this as some sort of
best practice for any context and should not be using this 
as it is without appropriate evaluation to their, so to say, 
specific programming context.

This page intends only to provide bit and piece of known ways  for
doing some sort of example and may not be fit for any other purpose.




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Event handling and Java Technology
How can I extend Java event handling code to suit
application specific event handling?

There are four parts to event handling, one is listener, 
second one is event object, the third one is the event 
container and fourth one is the event propagator.

Extension point for first two parts are provided by
Java api as java.util.EventListener and java.util.EventObject 
respectively. The third one (Event listener container) and
fourth one (event generator) has to be provided by programmer

Event generator should extend  event listener container,
and every event generator/source should add event listeners
added to it, and calls event methods and passes event object
associated with this event listener.

Let us implement a sample demo exercise:

A demo listener implemented as follows:

The first one is the event listener as follows:

public interface DemoListener extends
 java.util.EventListener
{
	public void demoEvent(DemoEvent dm);
}

and second one the event object as follows:

public class DemoEvent extends java.util.EventObject
{
	Object obj;
	public DemoEvent(Object source)
	{
		super(source);
		obj = source;

	}
	public Object getSource()
	{
		return obj;
	}
	......
}

The third part is the event container:

public class EventContainer
{
	private Vector repository = new Vector();
	DemoListener dl;
	public EventContainer()
	{

	}
	public void addDemoListener(DemoListener dl)
	{
		repository.addElement(dl);
	}
	public void notifyDemoEvent()
	{
		Enumeration enum = repository.elements();
		while(enum.hasMoreElements())
		{
			dl = (DemoListener)enum.nextElement();
			dl.demoEvent(new DemoEvent(this));
		}
	}
	......
}

The fourth one is the event listener implementor, that
implements event listener and implements event handling
code/method.

EventContainer adds implemented DemoListener and based
on certain event, notifyDemoEvent methods executes
demoEvent method for all the demo listeners in the
repository inside EventContainer.



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