1 import java.util.ArrayList; 2  3 //观察者模式 4 public class Observer { 5  6     public static void main(String[] args) { 7         //间谍007 8         Spy007 spy007 = new Spy007(); 9         //两个国家雇佣了00710         Country coutryA = new CuntryA("乙国",spy007);11         Country coutryB = new CuntryB("丙国",spy007);12         //007记住了两个国家13         spy007.Attach(coutryA);14         spy007.Attach(coutryB);15         //007发现了情报16         spy007.setIntelligence("甲国研制了核武器");17         //向两个国家汇报情况18         spy007.Notify();19     }20 }21 //抽象国家类22 abstract class Country{23     protected String countryName;24     protected Spy007 spy;25     //构造函数26     public Country(String countryName, Spy007 spy) {27         this.countryName = countryName;28         this.spy = spy;29     }30     //获取情报的抽象方法31     abstract void Update();32 }33 //具体的A类国家34 class CuntryA extends Country{35 36     public CuntryA(String countryName,Spy007 spy) {37         super(countryName, spy);38     }39     //获取情报的方法40     @Override41     void Update() {42         System.out.println(countryName+"得到情报："+spy.getIntelligence()+"决定于甲国建交");43         44     }45     46 }47 //具体的B类国家48 class CuntryB extends Country{49     public CuntryB(String countryName,Spy007 spy) {50         super(countryName,spy);51     }52 53     @Override54     void Update() {55         System.out.println(countryName+"得到情报："+spy.getIntelligence()+"决定于甲国开战");56     }57     58 }59 //间谍00760 class Spy007{61     private ArrayList
     
       countrys = new ArrayList
      
       ();62     //具体的情报63     private String intelligence;64     //进入国家65     public void Attach(Country country) {66         countrys.add(country);67     }68     //离开国家69     public void Detach(Country country) {70         countrys.remove(country);71     }72     //通知情报73     public void Notify() {74         for(Country c : countrys) {75             c.Update();76         }77     }78     //设定情报79     public void setIntelligence(String intelligence) {80         this.intelligence = intelligence;81     }82     //获取情报83     public String getIntelligence() {84         return intelligence;85     }86 }
      
     

输出：

　　  乙国得到情报：甲国研制了核武器决定于甲国建交

　　  丙国得到情报：甲国研制了核武器决定于甲国开战