eventhandler.java

sea是一个基于seda模式的实现。这个设计模式将系统分为很多stage。每个stage分布不同的任务（基于线程池）。通过任务流的方式提高系统的效率。

/*
 * Copyright (c) 2003, The Regents of the University of California, through
 * Lawrence Berkeley National Laboratory (subject to receipt of any required
 * approvals from the U.S. Dept. of Energy). All rights reserved.
 */
package gov.lbl.dsd.sea;

/**
 * The abstract base class of all asynchronous event handlers.
 * 
 * @author [e-mail]
 * @author $Author: gegles $
 * @version $Revision: 1.9 $, $Date: 2004/09/16 16:57:15 $
 */
public abstract class EventHandler {
	
	protected Stage stage = null; // the stage associated with this event handler

	protected EventHandler() {} // make constructor invisible in javadoc

	/** 
	 * Sets the stage associated with this event handler. 
	 */
	protected void setStage(Stage stage) {
		if (this.stage != null && this.stage != stage) 
				throw new IllegalArgumentException("Can't change immutable stage");
		
		this.stage = stage;
	}

	/** 
	 * Returns the stage associated with this event handler. 
	 */
	protected Stage getStage() {
		return this.stage;
	}

	/**
	 * Main entry point; called when an event handler should handle the given event.
	 */ 
	public abstract void handle(Object event);

	/**
	 * Called when the event handler's stage is started. This method should perform
	 * any initialization operations as required by the application. 
	 * The default implementation does nothing.
	 */
	public void onStart() {}
	
	/**
	 * Called when the event handler's stage is stopped.
	 * The default implementation does nothing.
	 */
	public void onStop() {}

}