观察者模式

/** 
 * 主题接口，所有的主题必须实现此接口 
 *  
 * @author zhy 
 *  
 */  
public interface Subject{  
    /** 
     * 注册一个观察着 
     *  
     * @param observer 
     */  
    public void registerObserver(Observer observer);  
  
    /** 
     * 移除一个观察者 
     *  
     * @param observer 
     */  
    public void removeObserver(Observer observer);  
  
    /** 
     * 通知所有的观察着 
     */  
    public void notifyObservers();  
  
} 

/** 
 * @author zhy 所有的观察者需要实现此接口 
 */  
public interface Observer{  
    public void update(String msg);  
  
} 

public class ObjectFor3D implements Subject  
{  
    private List<Observer> observers = new ArrayList<Observer>();  
    /** 
     * 3D彩票的号码 
     */  
    private String msg;  
  
    @Override  
    public void registerObserver(Observer observer)  
    {  
        observers.add(observer);  
    }  
  
    @Override  
    public void removeObserver(Observer observer)  
    {  
        int index = observers.indexOf(observer);  
        if (index >= 0)  
        {  
            observers.remove(index);  
        }  
    }  
  
    @Override  
    public void notifyObservers()  
    {  
        for (Observer observer : observers)  
        {  
            observer.update(msg);  
        }  
    }  
  
    /** 
     * 主题更新消息 
     *  
     * @param msg 
     */  
    public void setMsg(String msg)  
    {  
        this.msg = msg;  
          
        notifyObservers();  
    }  
  
}

public class Observer1 implements Observer  
{  
  
    private Subject subject;  
  
    public Observer1(Subject subject)  
    {  
        this.subject = subject;  
        subject.registerObserver(this);  
    }  
  
    @Override  
    public void update(String msg)  
    {  
        System.out.println("observer1 得到 3D 号码  -->" + msg + ", 我要记下来。");  
    }  
  
} 

public class Observer2 implements Observer  
{  
    private Subject subject ;   
      
    public Observer2(Subject subject)  
    {  
        this.subject = subject  ;  
        subject.registerObserver(this);  
    }  
      
    @Override  
    public void update(String msg)  
    {  
        System.out.println("observer2 得到 3D 号码 -->" + msg + "我要告诉舍友们。");  
    }  
}  

public class Test  
{  
    public static void main(String[] args)  
    {  
        //模拟一个3D的服务号  
        ObjectFor3D subjectFor3d = new ObjectFor3D();  
        //客户1  
        Observer observer1 = new Observer1(subjectFor3d);  
        Observer observer2 = new Observer2(subjectFor3d);  
  
        subjectFor3d.setMsg("20140420的3D号码是：127" );  
        subjectFor3d.setMsg("20140421的3D号码是：333" );  
          
    }  
}  

下面我们使用Java内置的类实现观察者模式：

public class SubjectFor3d extends Observable  
{  
    private String msg ;   
      
      
    public String getMsg()  
    {  
        return msg;  
    }  
  
  
    /** 
     * 主题更新消息 
     *  
     * @param msg 
     */  
    public void setMsg(String msg)  
    {  
        this.msg = msg  ;  
        setChanged();  
        notifyObservers();  
    }  
}  

public class SubjectForSSQ extends Observable  
{  
    private String msg ;   
      
      
    public String getMsg()  
    {  
        return msg;  
    }  
  
  
    /** 
     * 主题更新消息 
     *  
     * @param msg 
     */  
    public void setMsg(String msg)  
    {  
        this.msg = msg  ;  
        setChanged();  
        notifyObservers();  
    }  
}

public class Observer1 implements Observer  {  
  
    public void registerSubject(Observable observable)  
    {  
        observable.addObserver(this);  
    }  
  
    @Override  
    public void update(Observable o, Object arg)  
    {  
        if (o instanceof SubjectFor3d)  
        {  
            SubjectFor3d subjectFor3d = (SubjectFor3d) o;  
            System.out.println("subjectFor3d's msg -- >" + subjectFor3d.getMsg());  
        }  
  
        if (o instanceof SubjectForSSQ)  
        {  
            SubjectForSSQ subjectForSSQ = (SubjectForSSQ) o;  
            System.out.println("subjectForSSQ's msg -- >" + subjectForSSQ.getMsg());  
        }  
    }  
}  

public class Test  {  
    public static void main(String[] args)  
    {  
        SubjectFor3d subjectFor3d = new SubjectFor3d() ;  
        SubjectForSSQ subjectForSSQ = new SubjectForSSQ() ;  
          
        Observer1 observer1 = new Observer1();  
        observer1.registerSubject(subjectFor3d);  
        observer1.registerSubject(subjectForSSQ);  
          
          
        subjectFor3d.setMsg("hello 3d'nums : 110 ");  
        subjectForSSQ.setMsg("ssq'nums : 12,13,31,5,4,3 15");  
          
    }  
}