设计模式之Observer - 观察者模式

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

public class Client {

    /**
     * Test Observer Pattern
     * --
     * 
     */
    public static void main(String[] args) {
        NewsPublisher publisher = new NewsPublisher();
        //添加观察者对象
        publisher.addObserver(new SubscriberObserver());
        publisher.addObserver(new ManagerObserver());
        
        //发布新闻，触发通知事件
        publisher.publishNews("Hello news", "news body");
    }
}


/**
 * Subject ROLE
 * NewsPublisher: news publisher
 *
 */
class NewsPublisher extends Observable {
    public void publishNews(String newsTitle, String newsBody) {
        News news = new News(newsTitle, newsBody);
        setChanged();       //通过setChanged()方法标明对象的状态已发生变化
        
        System.out.println("News published:" + newsTitle);
        this.notifyObservers(news);   //通知各Observer，并发送一个名为news对象的消息
        
        //other process ... such as save news to database
    }
}

/**
 * Observer ROLE
 * 
 */
class SubscriberObserver implements Observer {
    
    public void update(Observable observee, Object param) {
        if (param instanceof News) {
            mail2Subscriber((News)param);
        }
    }
    
    private void mail2Subscriber(News news) {
        System.out.println("Mail to subscriber. A news published with title:" + news.getTitle());
    }
}

/**
 * Observer ROLE
 * 
 */
class ManagerObserver implements Observer {
    
    public void update(Observable observee, Object param) {
        if (param instanceof News) {
            mail2Manager((News)param);
        }
    }
    
    private void mail2Manager(News news) {
        System.out.println("Mail to Manager. A news published with title:" + news.getTitle());
    }
}

//data entity
class News {
    private String title;
    private String body;
    
    public News(String title, String body) {
        this.title = title;
        this.body = body;
    }
    
    public String getBody() {
        return body;
    }
    public void setBody(String body) {
        this.body = body;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}