观察者模式（一）

package com.ygl.observer;

 //抽象的主题角色

 public interface Watched {

public void addWatcher(Watcher watcher);

public void removeWatcher(Watcher watcher);

public void notifyWatchers(String str);
}
//******************************************
package com.ygl.observer;
 //抽象观察者
 public interface Watcher {
 public void update(String str);
 }//**************************************
package com.ygl.observer;


 import java.util.ArrayList;
 import java.util.List;


 public class RealWatched implements Watched{
private List<Watcher> list=new ArrayList<Watcher>();
@Override
public void addWatcher(Watcher watcher) {

list.add(watcher);
}


@Override
public void removeWatcher(Watcher watcher) {

list.remove(watcher);
}


@Override
public void notifyWatchers(String str) {

for(Watcher watcher:list){
watcher.update(str);
}
}


 }//****************************************
package com.ygl.observer;


 public class RealWatcher implements Watcher{


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

}


 }//***********************************
package com.ygl.observer;


 public class Test {
public static void main(String[] args) {
Watched girl=new RealWatched();
 
Watcher watcher1=new RealWatcher();
Watcher watcher2=new RealWatcher();
Watcher watcher3=new RealWatcher();
girl.addWatcher(watcher1);
girl.addWatcher(watcher2);
girl.addWatcher(watcher3);
 
girl.notifyWatchers("我很开心");
 
girl.removeWatcher(watcher2);
girl.notifyWatchers("不是很开心");
}
    
 }