java 观察者模式

/*
  @author com.tiantian
  @version 创建时间：2012-11-20 下午4:58:25
 /
public interface IWatched {
    public void addWatcher(IWatcher watcher);
    public void removeWatcher(IWatcher watcher);
    public void notifyWatchers(String msg);
}

/*
  @author com.tiantian
  @version 创建时间：2012-11-20 下午4:55:23
 /
public interface IWatcher {
    public void update(String msg);
}

/*
  @author com.tiantian
  @version 创建时间：2012-11-20 下午5:01:05
 /
public class Watched implements IWatched{
    private List<IWatcher> watchers = new ArrayList<IWatcher>();
    @Override
    public void addWatcher(IWatcher watcher) {
        watchers.add(watcher);
    }

    @Override
    public void removeWatcher(IWatcher watcher) {
        watchers.remove(watcher);
    }

    @Override
    public void notifyWatchers(String msg) {
        for(IWatcher watcher : watchers){
            watcher.update(msg);
        }
    }
}

/*
  @author com.tiantian
  @version 创建时间：2012-11-20 下午5:04:56
 /
public class Watcher implements IWatcher{

    @Override
    public void update(String msg) {
        System.out.println(msg);
    }
}

/*
  @author com.tiantian
  @version 创建时间：2012-11-20 下午5:05:26
 /
public class Test {
    public static void main(String[] args) {
        IWatched watched = new Watched();
        IWatcher watcher1 = new Watcher();
        IWatcher watcher2 = new Watcher();
        IWatcher watcher3 = new Watcher();
        watched.addWatcher(watcher1);
        watched.addWatcher(watcher2);
        watched.addWatcher(watcher3);
        watched.notifyWatchers(“I have been clicked!”);

        watched.removeWatcher(watcher1);
        watched.notifyWatchers(“what’s up”);
    }
}