<rt id="bn8ez"></rt>
<label id="bn8ez"></label>

  • <span id="bn8ez"></span>

    <label id="bn8ez"><meter id="bn8ez"></meter></label>

    sunfruit[請?jiān)L問http://www.fruitres.cn]

    --我相信JAVA能走得更遠(yuǎn) QQ:316228067

    [JAVA]用戶自定義事件監(jiān)聽

        --sunfruit

        用戶自定義事件

       

    User defined Event listeners java

    All of us who have used java.awt.event package in either applets
    or in Frames or in swing JFrame, shall agree to the fact that event
    propagation and listener concept is very very useful for capturing
    any action initiated either by user or by system, should be caught
    at the right place and without unneccessarily wasting time traversing
    through all the way from begining to end of source code just to know
    any takers for this event.



    This concept is implemented in form of MouseEvent, KeyEvent, WindowEvent so on so forth.

    JDK has given us a handle for creating our own event object and as well
    as event handling framework using java.util.EventObject and java.util.EventListener.

    You can imagine a scenario whereby you have to write an application, in
    which a email notification feature in a forum.

    Whenever a special event takes place , then your have to notify all the users
    who have registered themselves for this program.

    One solution is to use a Database and query all the users from the table
    and send notification to each and every user.
    But this is more of Database centric approach like old days thick client
    and server model.

    Think about the overhead on database and instead another solution is
    to create an event notification framework, whereby you have to create
    your own version of Event Object and Event Listeners.

    Event object represents the special event and all the users who register
    themselves for the event implements this Event listener.

    Let us take a more deeper plunge into this:

    1. Create a Demo event by creating a DemoEvent.java file that
    extends to java.util.EventObject.

    This class has a constructor that takes the event originator object (DemoSource).
    and a method getSource(), that gives the reference to the object that originated
    this event.

    DemoEvent.java
    
    package demo.listener;
    
    import java.util.EventObject;
    
    public class DemoEvent extends EventObject
    {
    	Object obj;
    	public DemoEvent(Object source)
    	{
    		super(source);
    		obj = source;
    
    	}
    	public Object getSource()
    	{
    		return obj;
    	}
    	public void say()
    	{
    		System.out.println("This is say method...");
    	}
    
    }
    
    


    2. Create the source of event notification file DemoSource.java
    It has a java.util.Vector that acts like a repository for storing all the
    listeners to the events this source provides.

    It has two other common method such as addListener(..) is to add any
    new user to this event.

    And notifyDemoEvent(..) is to alert all the users about this perticular event
    occurance.

    DemoEvent.java
    
    package demo.listener;
    import java.util.*;
    
    public class DemoSource
    {
    	private Vector repository = new Vector();
    	DemoListener dl;
    	public DemoSource()
    	{
    
    	}
    	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));
    		}
    	}
    }
    
    


    3. Define a listener interface that extends to java.util.EventListener
    and contains the method for invoking the Event, here it is demoEvent(DemoEvent de).

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



    4. Define all the users, who want to listen to this events.
    These objects should implement DemoListener, to be able to
    capture the event propagated from DemoSource.java.

    Listener1.java
    
    package demo.listener;
    
    public class Listener1 implements DemoListener
    {
    	public void demoEvent(DemoEvent de)
    	{
    		System.out.println("Inside listener1...");
    	}
    }
    
    


    Listener2.java
    
    package demo.listener;
    
    public class Listener2 implements DemoListener
    {
    	public void demoEvent(DemoEvent de)
    	{
    		System.out.println("Inside listener2...");
    	}
    }
    
    

    Listener3.java
    
    package demo.listener;
    
    public class Listener3 implements DemoListener
    {
    	public void demoEvent(DemoEvent de)
    	{
    		System.out.println("Inside listener3...");
    	}
    }
    
    


    5. Now it time to write the client for testing this Framework.
    Create a client such as TestDemo.java and create a DemoSource
    object and all the users such as Listener1, Listener2, Listener3.
    And add all these listeners to the demo source by using the addDemoListener(..).
    When the notifyDemoEvent(..) is called on the demo source object,
    the event gets notified to all the users (listener1, listener2, listener3)
    and  the  output comes out to be

    Inside listener1...
    Inside listener2...
    Inside listener3...


    TestDemo.java
    
    package demo.listener;
    
    public class TestDemo
    {
    	DemoSource ds;
    
    	public TestDemo()
    	{
    		try{
    			ds = new DemoSource();
    			Listener1 l1 = new Listener1();
    			Listener2 l2 = new Listener2();
    			Listener3 l3 = new Listener3();
    
    			ds.addDemoListener(l1);
    			ds.addDemoListener(l2);
    			ds.addDemoListener(l3);
    
    			ds.notifyDemoEvent();
    
    		}catch(Exception ex){ex.printStackTrace();}
    	}
    
    	public static void main(String args[])
    	{
    		new TestDemo();
    	}
    }
    

    posted on 2006-02-19 17:58 sunfruit 閱讀(3543) 評論(0)  編輯  收藏 所屬分類: JAVA SE & EE

    主站蜘蛛池模板: 国产成人综合久久精品免费| 特级做A爰片毛片免费69 | 亚洲国产精品13p| 亚洲成在人线在线播放无码| 亚洲精品动漫免费二区| 亚洲一区电影在线观看| 手机在线看永久av片免费| 亚洲二区在线视频| 久久久www成人免费毛片| 亚洲熟妇av午夜无码不卡| 在线精品免费视频| 色天使亚洲综合一区二区| 婷婷亚洲天堂影院| 精品国产污污免费网站入口在线| 久久国产成人精品国产成人亚洲| 你懂得的在线观看免费视频| 久久久久亚洲av无码专区蜜芽| 小草在线看片免费人成视久网| 久久久久亚洲av无码专区| 久久精品无码一区二区三区免费 | 鲁大师在线影院免费观看| 中文字幕亚洲色图| 手机在线免费视频| 美女被艹免费视频| 亚洲自偷自偷在线制服| 69pao强力打造免费高清| 亚洲一日韩欧美中文字幕在线| 国产精品久久久久影院免费| eeuss免费影院| 91亚洲va在线天线va天堂va国产| 日韩不卡免费视频| 美女视频黄频a免费| 亚洲av无码片在线播放| 四虎国产精品免费久久| 黄色毛片免费观看| 亚洲人成电影福利在线播放| 好先生在线观看免费播放| selaoban在线视频免费精品| 亚洲欧洲自拍拍偷综合| 国产精品免费视频播放器| 久久久久久一品道精品免费看|