观察者模式

abstract class Subject {
    private Vector<Observer> obs = new Vector<Observer>();

    public void addObserver(Observer object) {
        this.obs.add(object);
    }

    public void delObserver(Observer object) {
        this.obs.remove(object);
    }

    protected void notifyObserver() {
        for (Observer o : obs) {
            o.update();
        }
    }

    public abstract void doSomething();
}

class ConcreteSubject extends Subject {

    @Override
    public void doSomething() {
        // TODO Auto-generated method stub
        System.out.println("Start");
        this.notifyObserver();
    }

}

interface Observer {
    public void update();
}

class ConcreteObserver1 implements Observer {

    @Override
    public void update() {
        // TODO Auto-generated method stub
        System.out.println("ConcreteObserver1  start");
    }

}

class ConcreteObserver2 implements Observer {

    @Override
    public void update() {
        // TODO Auto-generated method stub
        System.out.println("ConcreteObserver2  start");
    }

}
public class ObserverMode {
     public static void main(String[] args){
         Subject sub = new ConcreteSubject();
         sub.addObserver(new ConcreteObserver1());
         sub.addObserver(new ConcreteObserver2());
         sub.doSomething();
     }
}