一、java自带的观察者模式

package com.test.observer;

import java.util.Observable;

public class ServerManager extends Observable {
     private int data = 0;    
     public int getData(){         return data;    }   
     public void setData(int i){ 
         if(this.data != i){ this.data = i;setChanged();}  
         notifyObservers();  //只有在setChange()被调用后，notifyObservers()才会去调用update()，否则什么都不干。  } }
     }

}

import java.util.Observable;
import java.util.Observer;

public class AObserver implements Observer {
    
    public AObserver(ServerManager sm) {
        super();
        // TODO Auto-generated constructor stub
        sm.addObserver(this);　　//注册加入观察者
    }

    @Override
    public void update(Observable arg0, Object arg1) {
        System.out.println("AObserver receive:Data has changed to "+((ServerManager) arg0).getData());

    }

}

import java.util.Observable;
import java.util.Observer;

public class BObserver implements Observer {
    
    public BObserver(ServerManager sm) {
        super();
        sm.addObserver(this);　　//注册加入观察者
    }

    @Override
    public void update(Observable o, Object arg) {
        // TODO Auto-generated method stub
        System.out.println("BObserver receive:Data has changed to "+((ServerManager) o).getData());
    }

}

public class TestDemo {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ServerManager sm = new ServerManager();
        AObserver a    = new AObserver(sm);
        BObserver b = new BObserver(sm);
        sm.setData(5);
        sm.deleteObserver(a);　　//注销观察者，以后被观察者有数据变化就不再通知这个已注销的观察者
        sm.setData(10);
    }

}