1.觀察者接口及實現類

//一個Observer接口：
1.public interface Observer {  
2.    public void update();  
3.}  

//兩個實現類：
1.public class Observer1 implements Observer {  
2.  
3.    @Override  
4.    public void update() {  
5.        System.out.println("observer1 has received!");  
6.    }  
7.}  
1.public class Observer2 implements
 
 Observer {  
2.  
3.    @Override  
4.    public void update() {  
5.        System.out.println("observer2 has received!");  
6.    }  
7.  
8.}  

2.訂閱者接口及實現類

//訂閱者接口
public interface Subject {  
2.      
3.    /*增加觀察者*/  
4.    public void add(Observer observer);  
5.      
6.    /*刪除觀察者*/  
7.    public
 
 void del(Observer observer);  
8.      
9.    /*通知所有的觀察者*/  
10.    public void notifyObservers();  
11.      
12.    /*自身的操作*/  
13.    public void operation();  
14.}  
//實現接口的抽象類
1.public abstract class AbstractSubject implements Subject {  
2.  
3.    private Vector<Observer> vector = new Vector<Observer>();  
 
4.    @Override  
5.    public void add(Observer observer) {  
6.        vector.add(observer);  
7.    }  
8.  
9.    @Override  
10.    public void del(Observer observer) {  
11.        vector.remove(observer);  
12.    }  
13.  
14.    @Override  
15.    public void notifyObservers() {  
16.        Enumeration<Observer> enumo = vector.elements();//放入觀察者的集合，並循環遍歷來調用（通知）觀察者的update（）方法
17.        while(enumo.hasMoreElements()){  
18.            enumo.nextElement().update();  
19.        }  
20.    }  
21.}  
//繼承抽象類的具體實現類
1.public class MySubject extends AbstractSubject {  
2.  
3.    @Override  
4.    public void operation() {  
5.        System.out.println("update self!");  
6.        notifyObservers();  
7.    }  
8.  
9.}  

3.測試使用

//將所有 的觀察者放入集合並調用訂閱函數
public class ObserverTest {  
2.  
3.    public static void main(String[] args) {  
4.        Subject sub = new MySubject();  
5.        sub.add(new Observer1());  
6.        sub.add(new Observer2());  
7.          
8.        sub.operation();  
9.    }  
10.  
11.} 

輸出結果

update self!
observer1 has received!
observer2 has received!

觀察者設計模式