【GOF23设计模式】观察者模式

来源：http://www.bjsxt.com/ 
一、【GOF23设计模式】_观察者模式、广播机制、消息订阅、网络游戏对战原理

 package com.test.observer;

 import java.util.ArrayList;
 import java.util.List;

 public class Subject {
     protected List<Observer> list = new ArrayList<Observer>();

     public void registerObserver(Observer obs){
         list.add(obs);
     }
     public void removeObserver(Observer obs){
         list.remove(obs);
     }

     //通知所有的观察者更新状态
     public void notjfyAllObservers(){
         for (Observer obs : list) {
             obs.update(this);
         }
     }
 }

 package com.test.observer;

 public class ConcreteSubject extends Subject{
     private int state;

     public int getState() {
         return state;
     }

     public void setState(int state) {
         this.state = state;
         //主题对象(目标对象)的值发生了变化，请通知所有的观察者
         this.notjfyAllObservers();
     }
 }

 package com.test.observer;

 public interface Observer {
     void update(Subject subject);
 }

 package com.test.observer;

 public class ObserverA implements Observer{
     private int myState;//myState需要跟目标对象的state值保持一致

     public int getMyState() {
         return myState;
     }

     public void setMyState(int myState) {
         this.myState = myState;
     }

     @Override
     public void update(Subject subject) {
         myState = ((ConcreteSubject)subject).getState();
     }
 }

 package com.test.observer;

 public class Client {
     public static void main(String[] args) {
         //目标对象
         ConcreteSubject subject = new ConcreteSubject();

         //创建多个观察者
         ObserverA obs1 = new ObserverA();
         ObserverA obs2 = new ObserverA();
         ObserverA obs3 = new ObserverA();

         //将这三个观察者添加到subject对象的观察者队伍中
         subject.registerObserver(obs1);
         subject.registerObserver(obs2);
         subject.registerObserver(obs3);

         //改变subject的状态
         subject.setState(3000);
         System.out.println("#################");
         //我们看看，观察者的状态是不是也发生了变化
         System.out.println(obs1.getMyState());
         System.out.println(obs2.getMyState());
         System.out.println(obs3.getMyState());

         //改变subject的状态
         subject.setState(30);
         System.out.println("#################");
         //我们看看，观察者的状态是不是也发生了变化
         System.out.println(obs1.getMyState());
         System.out.println(obs2.getMyState());
         System.out.println(obs3.getMyState());
     }
 }

控制台输出：
#################
3000
3000
3000
#################
30
30
30

二、【GOF23设计模式】_观察者模式、obserable类和observer接口、应用场景总结

 package com.test.observer2;

 import java.util.Observable;
 /**
  * 目标对象
  */
 public class ConcreteSubject extends Observable{
     private int state;

     public int getState() {
         return state;
     }

     public void setState(int state) {
         this.state = state;
     }

     public void set(int s){
         state = s;  //目标对象的状态发生了改变

         setChanged();   //表示目标对象已经做了更改
         notifyObservers(state); //通知所有的观察者
     }
 }

 package com.test.observer2;

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

 public class ObserverA implements Observer{
     private int myState;

     public int getMyState() {
         return myState;
     }

     public void setMyState(int myState) {
         this.myState = myState;
     }

     @Override
     public void update(Observable o, Object arg) {
         myState = ((ConcreteSubject)o).getState();
     }
 }

 package com.test.observer2;

 public class Client {
     public static void main(String[] args) {
         //创建目标对象Obserable
         ConcreteSubject subject = new ConcreteSubject();

         //创建观察者
         ObserverA obs1 = new ObserverA();
         ObserverA obs2 = new ObserverA();
         ObserverA obs3 = new ObserverA();

         //将上面三个观察者对象添加到目标对象subject的观察者容器中
         subject.addObserver(obs1);
         subject.addObserver(obs2);
         subject.addObserver(obs3);

         //改变subject对象的状态
         subject.set(3000);
         System.out.println("==================状态修改了");
         //观察者的状态发生了变化
         System.out.println(obs1.getMyState());
         System.out.println(obs2.getMyState());
         System.out.println(obs3.getMyState());

         //改变subject对象的状态
         subject.set(600);
         System.out.println("==================状态修改了");
         //观察者的状态发生了变化
         System.out.println(obs1.getMyState());
         System.out.println(obs2.getMyState());
         System.out.println(obs3.getMyState());
     }
 }

控制台输出：
==================状态修改了
3000
3000
3000
==================状态修改了
600
600
600