观察者模式：定义了对象之间的一对多依赖，这样依赖，当一个对象改变状态时，它的所有依赖者都会收到通知并自动更新。

 

 

 

下面举一个具体例子：

两个观察者，BinaryObserver的update将setState传入的整数转换成二进制，OctaObserver则是转成八进制

 

interface Subject {       private List
     
       observers;    public void registerObserver(Observer o);    public void removeObserver(Observer o);     public void notifyAllObservers();}
     

 

public class ConcreteSubject implements Subject{       private List
     
       observers       = new ArrayList
      
       ();   private int state;   public int getState() {      return state;   }   public void setState(int state) {      this.state = state;      notifyAllObservers();   }   public void registerObserver(Observer observer){      observers.add(observer);           }    public void removeObserver(Observer observer){       int i = observers.indexOf(observer);       if(i >= 0)              observers.remove(i);    }   public void notifyAllObservers(){      for (Observer observer : observers) {         observer.update();      }   }     }
      
     

 

abstract Observer {   public abstract void update();}

public class BinaryObserver implements Observer{　 Subject subject;   public BinaryObserver(Subject subject){      this.subject = subject;      this.subject.attach(this);   }   @Override   public void update() {      System.out.println( "Binary String: "       + Integer.toBinaryString( subject.getState() ) );    }}

 

public class OctalObserver implements Observer{   Subject subject;   public OctalObserver(Subject subject){      this.subject = subject;      this.subject.attach(this);   }   @Override   public void update() {     System.out.println( "Octal String: "      + Integer.toOctalString( subject.getState() ) );    }}

 

测试代码：

Subject subject = new ConcreteSubject();Observer o = new OctalObserver(subject);Observer b = new BinaryObserver(subject); subject.registerObserver(o); subject.registerObserver(b);subject.setState(15);subject.setState(10);

 

在Swing中有使用到观察者模式，比如JButton的addActionListener方法。