Java之觀察者模式

1．概念

        定義一種一對多的依賴關係，當一個對象的狀態發生改變時，所有依賴於它的對象都得到通知並被自動更新。

2．UML圖

3．代碼

interface Subject 
{ 
public void attach(Observer observer); 
public void detach(Observer observer); 
void notifyObservers(); 
} 

public class ConcreteSubject implements Subject
{
private Vector observersVector = new Vector(); 

public void attach(Observer observer) { 
       observersVector.addElement(observer); 
   } 

public void detach(Observer observer){ 
       observersVector.removeElement(observer); 
   } 

public void notifyObservers(){ 
       Enumeration enumeration = observersVector.clone()).elements();
while (enumeration.hasMoreElements()){ 
        ((Observer)enumeration.nextElement()).update(); 
    } 
  } 
} 

public interface Observer { 
void update(); 
} 

public class ConcreteObserver1 implements Observer{ 
public void update() { 
     System.out.println("Obsver1 execute");
   } 
} 

public class ConcreteObserver2 implements Observer{ 
public void update() { 
     System.out.println("Obsver2 execute");
   } 
} 

public class Main {   
public static void main(String[] args) {   
        ConcreteSubject concreteSubject = new ConcreteSubject ();   

        ConcreteObserver1 observer1 = new ConcreteObserver1();   
        ConcreteObserver2 observer2 = new ConcreteObserver2();   

        generator.addObserver(observer1);   
        generator.addObserver(observer2);   

        concreteSubject.notifyObservers();  
    }   
}  

4．應用情境

   當對一個對象的改變需要同時改變其它對象,依賴於它的對象都需要改變時。