//抽象主题角色类
public abstract class Subject {/*** 用来保存注册的观察者对象*/private    List<Observer> list = new ArrayList<Observer>();/*** 注册观察者对象* @param observer    观察者对象*/public void attach(Observer observer){list.add(observer);System.out.println("Attached an observer");}/*** 删除观察者对象* @param observer    观察者对象*/public void detach(Observer observer){list.remove(observer);}/*** 通知所有注册的观察者对象*/public void nodifyObservers(String newState){for(Observer observer : list){observer.update(newState);}}
}
//具体主题角色类
public class ConcreteSubject extends Subject{private String state;public String getState() {return state;}public void change(String newState){state = newState;System.out.println("主题状态为：" + state);//状态发生改变，通知各个观察者this.nodifyObservers(state);}
}
//抽象观察者角色类
public interface Observer {/*** 更新接口* @param state    更新的状态*/public void update(String state);
}
//具体观察者角色类
public class ConcreteObserver implements Observer {//观察者的状态private String observerState;@Overridepublic void update(String state) {/*** 更新观察者的状态，使其与目标的状态保持一致*/observerState = state;System.out.println("状态为："+observerState);}
}
//客户端类
public class Client {public static void main(String[] args) {//创建主题对象ConcreteSubject subject = new ConcreteSubject();//创建观察者对象Observer observer = new ConcreteObserver();//将观察者对象登记到主题对象上
        subject.attach(observer);//改变主题对象的状态subject.change("new state");}
}

public interface Observer {/*** 更新接口* @param subject 传入主题对象，方面获取相应的主题对象的状态*/public void update(Subject subject);
}
//拉模型的具体观察者类
public class ConcreteObserver implements Observer {//观察者的状态private String observerState;@Overridepublic void update(Subject subject) {/*** 更新观察者的状态，使其与目标的状态保持一致*/observerState = ((ConcreteSubject)subject).getState();System.out.println("观察者状态为："+observerState);}}
//拉模型的抽象主题类,拉模型的抽象主题类主要的改变是nodifyObservers()方法。在循环通知观察者的时候，也就是循环调用观察者的update()方法的时候，传入的参数不同了。
public abstract class Subject {/*** 用来保存注册的观察者对象*/private    List<Observer> list = new ArrayList<Observer>();/*** 注册观察者对象* @param observer    观察者对象*/public void attach(Observer observer){list.add(observer);System.out.println("Attached an observer");}/*** 删除观察者对象* @param observer    观察者对象*/public void detach(Observer observer){list.remove(observer);}/*** 通知所有注册的观察者对象*/public void nodifyObservers(){for(Observer observer : list){observer.update(this);}}
}
//拉模型的具体主题类,跟推模型相比，有一点变化，就是调用通知观察者的方法的时候，不需要传入参数了。
public class ConcreteSubject extends Subject{private String state;public String getState() {return state;}public void change(String newState){state = newState;System.out.println("主题状态为：" + state);//状态发生改变，通知各个观察者this.nodifyObservers();}
}

public interface Observer {void update(Observable o, Object arg);
}

public class Observable {private boolean changed = false;private Vector obs;/** Construct an Observable with zero Observers. */public Observable() {obs = new Vector();}/*** 将一个观察者添加到观察者聚集上面*/public synchronized void addObserver(Observer o) {if (o == null)throw new NullPointerException();if (!obs.contains(o)) {obs.addElement(o);}}/*** 将一个观察者从观察者聚集上删除*/public synchronized void deleteObserver(Observer o) {obs.removeElement(o);}public void notifyObservers() {notifyObservers(null);}/*** 如果本对象有变化（那时hasChanged 方法会返回true）* 调用本方法通知所有登记的观察者，即调用它们的update()方法* 传入this和arg作为参数*/public void notifyObservers(Object arg) {Object[] arrLocal;synchronized (this) {if (!changed)return;arrLocal = obs.toArray();clearChanged();}for (int i = arrLocal.length-1; i>=0; i--)((Observer)arrLocal[i]).update(this, arg);}/*** 将观察者聚集清空*/public synchronized void deleteObservers() {obs.removeAllElements();}/*** 将“已变化”设置为true*/protected synchronized void setChanged() {changed = true;}/*** 将“已变化”重置为false*/protected synchronized void clearChanged() {changed = false;}/*** 检测本对象是否已变化*/public synchronized boolean hasChanged() {return changed;}/*** Returns the number of observers of this <tt>Observable</tt> object.** @return  the number of observers of this object.*/public synchronized int countObservers() {return obs.size();}
}

//被观察者Watched类
public class Watched extends Observable{private String data = "";public String getData() {return data;}public void setData(String data) {if(!this.data.equals(data)){this.data = data;setChanged();}notifyObservers();}
}
//观察者类
public class Watcher implements Observer{    public Watcher(Observable o){o.addObserver(this);}   @Overridepublic void update(Observable o, Object arg) {     System.out.println("状态发生改变：" + ((Watched)o).getData());}
}
//测试类
public class Test {public static void main(String[] args) {//创建被观察者对象Watched watched = new Watched();//创建观察者对象，并将被观察者对象登记Observer watcher = new Watcher(watched);//给被观察者状态赋值watched.setData("start");watched.setData("run");watched.setData("stop");}
}