观察者模式

  个人理解：就是一个类拥有另一个类的引用 ，其中前者是被观察者，后者是观察者

  当被观察者发生状态改变的时候，观察者发生变化。

 

 1 观察者接口

public interface Watcher {
	public void update( String str);
}

 2 观察者接口的实现类

 

public class ConcreateWatcher implements Watcher{
	@Override
	public void update(String str) {
		System.out.println("观察者收到    : " + str );
	}
}

 

  3 被观察者接口

 

public interface Watched {
	public void addWatcher(Watcher watcher);
	public void removeWatcher(Watcher watcher);
	public void notifyWatchers(String str);
}

 

4   被观察者接口的实现类

public class concreateWatched implements Watched{

	private  List <Watcher> list = new ArrayList<Watcher>();
	@Override
	public void addWatcher(Watcher watcher) {
		list.add(watcher);
	}

	@Override
	public void notifyWatchers(String str) {
		for(Watcher watcher :list ){
			watcher.update(str);
		}
	}
	@Override
	public void removeWatcher(Watcher watcher) {
		list.remove(watcher );
	}
}

 

  5 测试类 

 

public class TestWatcher {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		//被观察者 
		Watched girl = new concreateWatched();
		
		//创建三个 观察者  
		Watcher watcher1 = new ConcreateWatcher();
		Watcher watcher2 = new ConcreateWatcher();
		Watcher watcher3 = new ConcreateWatcher();
		
		//被观察者中 添加观察者监听器  
		girl.addWatcher(watcher1);
		girl.addWatcher(watcher2);
		girl.addWatcher(watcher3);
		
		//被观察者 通知观察者 状态改变 
		girl.notifyWatchers( "开心 爽");
		//移除一个观察者 
		girl.removeWatcher(watcher2);
		
		girl.notifyWatchers("  不爽");
		
	}

}