吴裕雄--天生自然轻量级JAVA EE企业应用开发Struts2Sping4Hibernate整合开发学习笔记：企业应用开发的思考和策略_Observer

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

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public abstract class Observable
{
    // 用一个List来保存该对象上所有绑定的事件监听器
    List<Observer> observers =
        new ArrayList<Observer>();
    // 定义一个方法，用于从该主题上注册观察者
    public void registObserver(Observer o)
    {
        observers.add(o);
    }
    // 定义一个方法，用于从该主题中删除观察者
    public void removeObserver(Observer o)
    {
        observers.remove(o);
    }
    // 通知该主题上注册的所有观察者
    public void notifyObservers(Object value)
    {
        // 遍历注册到该被观察者上的所有观察者
        for (Observer o : observers)
        {
            // 显式调用每个观察者的update()方法
            o.update(this , value);
        }
    }
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public interface Observer
{
    void update(Observable o , Object arg);
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class PriceObserver implements Observer
{
    // 实现观察者必须实现的update()方法
    public void update(Observable o , Object arg)
    {
        if(arg instanceof Double)
        {
            System.out.println("价格观察者:" +
                o + "物品价格已经改变为: " + arg);
        }
    }
}

import java.util.Iterator;
/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class Product extends Observable
{
    // 定义两个成员变量
    private String name;
    private double price;
    // 无参数的构造器
    public Product(){}
    public Product(String name , double price)
    {
        this.name = name;
        this.price = price;
    }
    public String getName()
    {
        return name;
    }
    //当 程序调用name的setter方法来修改Product的name成员变量时
    // 程序自然触发该对象上注册的所有观察者
    public void setName(String name)
    {
        this.name = name;
        notifyObservers(name);
    }
    public double getPrice()
    {
        return price;
    }
    // 当程序调用price的setter方法来修改Product的price成员变量时
    // 程序自然触发该对象上注册的所有观察者
    public void setPrice(double price)
    {
        this.price = price;
        notifyObservers(price);
    }
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class Test
{
    public static void main(String[] args)
    {
        // 创建一个被观察者对象
        Product p = new Product("电视机" , 176);
        // 创建两个观察者对象
        NameObserver no = new NameObserver();
        PriceObserver po = new PriceObserver();
        // 向被观察对象上注册两个观察者对象
        p.registObserver(no);
        p.registObserver(po);
        // 程序调用setter方法来改变Product的name和price成员变量
        p.setName("书桌");
        p.setPrice(345f);
    }
}

import javax.swing.JFrame;
import javax.swing.JLabel;
/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2016, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class NameObserver implements Observer
{
    // 实现观察者必须实现的update()方法
    public void update(Observable o , Object arg)
    {
        if (arg instanceof String )
        {
            // 将产品名称改变值放在name中
            String name = (String)arg;
            // 启动一个JFrame窗口来显示被观察对象的状态改变
            JFrame f = new JFrame("观察者");
            JLabel l = new JLabel("名称改变为：" + name);
            f.add(l);
            f.pack();
            f.setVisible(true);
            System.out.println("名称观察者:" +
                o + "物品名称已经改变为: " + name);
        }
    }
}