/***观察者接口*/
public interface Observer {void update(Subject subject);//观察者接收一个推送过来的主题}//============================/***观察者具体实现类*/
public class ObserverImpl implements Observer {private int state; //拥有与主体一致的状态，用于接收订阅的主题内容 public int getState() {return state;}public void setState(int state) {this.state = state;}@Overridepublic void update(Subject subject) {this.state=((ConcreteSubject)subject).getState();//在具体观察者中进行同步状态更新}}

/*** 主体的基类，定义了一些公用方法，没有具体主题，也可以定义成抽象类*/
public class Subject {public List<Observer> list=new ArrayList<Observer>();//在主体方定义一个容器存放注册的观察者public void registerObserver(Observer obs){list.add(obs);//注册观察者，即把需要订阅的观察者加进容器中}public void removeObserver(Observer obs){list.remove(obs);//移除观察者}//主题发生变化时，通知所有观察者进行更新public void notifyAllObservers(List<Observer> list){for (Observer observer : list) {observer.update(this);}}}//=================================================/***有具体主题的子类*/
public class ConcreteSubject extends Subject {private int state;//模拟一个具体主题public int getState() {return state;}public void setState(int state) {this.state = state;this.notifyAllObservers(list);//此步为关键，当主题发生变化时，主题中注册的观察者的状态也跟着进行更新}   }

     public static void main(String[] args) {ConcreteSubject concreteSubject = new ConcreteSubject();//目标主题，发布者ObserverImpl observer1=new ObserverImpl();ObserverImpl observer2=new ObserverImpl();ObserverImpl observer3=new ObserverImpl();concreteSubject.registerObserver(observer1);//注册观察者concreteSubject.registerObserver(observer2);concreteSubject.registerObserver(observer3); concreteSubject.setState(1000);//目标主题状态为1000System.out.println(observer1.getState());System.out.println(observer2.getState());System.out.println(observer3.getState());//观察者的值也都为1000concreteSubject.setState(2000);//目标主题状态值发生改变System.out.println(observer1.getState());System.out.println(observer2.getState());System.out.println(observer3.getState());//观察者的值也改为2000}

/*** 继承JDK的Observable类实现主题*/
public class ConcreteSubject extends Observable{private int state;public int getState() {return state;}public void setState(int state) {this.state = state;super.setChanged();//当次属性发生改变时，调用基类的setChanged()方法表示当前观察者有改变，//主要改变super.hasChanged()方法返回值，观察者可以通过此值判断目标对象是否已改变super.notifyObservers(this.state);//把当前发生改变的对象通知各个观察者}
}//===================================================/***实现JDK的观察者接口，实现更新方法*/
public class ObserverImpl implements Observer {private int state;   public int getState() {return state;}public void setState(int state) {this.state = state;}@Overridepublic void update(Observable o, Object obj) {setState(((ConcreteSubject)o).getState());//this.state =Integer.parseInt((String)obj);//也可以直接通过传递过来的参数赋值}
}//==================================================public static void main(String[] args) {ConcreteSubject subject=new ConcreteSubject();ObserverImpl observer1=new ObserverImpl();ObserverImpl observer2=new ObserverImpl();ObserverImpl observer3=new ObserverImpl();subject.addObserver(observer1);subject.addObserver(observer2);subject.addObserver(observer3);subject.setState(10);System.out.println(observer1.getState());System.out.println(observer2.getState());System.out.println(observer3.getState());//观察者的值也都为1000subject.setState(2000);//目标主题状态值发生改变System.out.println(observer1.getState());System.out.println(observer2.getState());System.out.println(observer3.getState());//观察者的值也改为2000}