Observer模式

import java.util.*;
interface ISubject {
	public void attach(IObserver observer);
	public void detach(IObserver observer);
	public void notifyObservers();
	public void setState(int state);
}
interface IObserver {
	public void update();
}
public class Observer {

	public static void main(String[] args) {
		ISubject sub = new Subject();
		sub.attach(new ObserverOne());
		sub.attach(new ObserverTwo());
		
		sub.setState(10);
	}
}

class Subject implements ISubject {
	private int state = 0;
	private List<IObserver> observers = new ArrayList<IObserver>();
	
	public int getState() {
		return state;
	}
	@Override public void setState(int state) {
		this.state = state;
		this.notifyObservers();
	}
	@Override public void attach(IObserver observer) {
		this.observers.add(observer);
	}
	@Override public void detach(IObserver observer) {
		this.observers.remove(observer);
	}
	@Override public void notifyObservers() {
		for (IObserver ob : observers)
			ob.update();
	}
}
class ObserverOne implements IObserver {
	@Override public void update() {
		System.out.println("ObserverOne receive notify...");
	}
}
class ObserverTwo implements IObserver {
	@Override public void update() {
		System.out.println("ObserverTwo receive notify...");
	}
}

* 定义对象间的一种一对多的依赖关系,当一个对象的状态发生改变时, 所有依赖于它的对象都得到通知并被自动更新。