watcher.java

来自「《Java与模式》一书的源代码」· Java 代码 · 共 18 行

package com.javapatterns.observer.watching;

import java.util.Observable;
import java.util.Observer;

public class Watcher implements Observer
{
    public Watcher(Watched wa)
    {
        wa.addObserver(this);
    }

    public void update(Observable ob, Object arg)
    {
        System.out.println("Data has been changed to:  '" + ((Watched)ob).retrieveData() + "'");
    }
}