Observer模式 （或称为Publish-Subscribe模式)

1.Subject.java

public interface Subject{public void notifyObserver();public void addObserver(Observer o);public void removeObserver(Observer o);} 2.Display.java

public interface Display{void display();} 3.Observer.java

public interface Observer{public void update();} 4.Cat.java

import java.util.*;public class Cat implements Subject{private ArrayList observers;public Cat(){observers=new ArrayList();}public void addObserver(Observer o){observers.add(o);}public void removeObserver(Observer o){int i=observers.indexOf(o);if(i>0){observers.remove(o);}}public void notifyObserver(){for(int i=0;i<observers.size();i++){Observer observer=(Observer)observers.get(i);observer.update();}}public void shout(){System.out.println("Cat is shouting");notifyObserver();}}

5.Mouse.java

public class Mouse implements Observer,Display{private Cat cat;public Mouse(Cat cat){this.cat=cat;cat.addObserver(this);}public void update(){display();}public void display(){System.out.println("Mouse is sliping away.");}} 6.Host.java

public class Host implements Observer,Display{private Cat cat;public Host(Cat cat){this.cat=cat;cat.addObserver(this);}public void update(){display();}public void display(){System.out.println("Host is awaken");}} 7.Test.java

public class Test{public static void main(String[] args){Cat cat=new Cat();Mouse mouse=new Mouse(cat);Host host=new Host(cat);cat.shout();}}

 

分析：

 

声明了接口Subject,定义了三个函数,分别用来

1.通知观察者

2.注册观察者

3.注销观察者

 

接口Display定义了函数用来表示采取行动的接口

 

接口Observer定义了函数用来表示Subject改变之后采取的行动

 

整个例子Cat是主题，Host，Mouse是观者者，简单的一句话总结就是：

 

猫叫了一声，老鼠跑了，主人醒了