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java-设计模式-创建模式-观察者模式observer

public interface Subject {    public void registerObserver(Observer o);    public void removeObserver(Observer o);    public void notifyAllObservers();}

Observer接口

public interface Observer {    public void update(Subject s);}

import java.util.ArrayList; public class HeadHunter implements Subject{     //define a list of users, such as Mike, Bill, etc.    private ArrayList
    
      userList;    private ArrayList
     
       jobs;     public HeadHunter(){        userList = new ArrayList
      
       ();        jobs = new ArrayList
       
        ();    }     @Override    public void registerObserver(Observer o) {        userList.add(o);    }     @Override    public void removeObserver(Observer o) {}     @Override    public void notifyAllObservers() {        for(Observer o: userList){            o.update(this);        }    }     public void addJob(String job) {        this.jobs.add(job);        notifyAllObservers();    }     public ArrayList
        
          getJobs() { return jobs; } public String toString(){ return jobs.toString(); }}
        
       
      
     
    

JobSeeker是一个观察者：

public class JobSeeker implements Observer {     private String name;     public JobSeeker(String name){        this.name = name;    }    @Override    public void update(Subject s) {        System.out.println(this.name + " got notified!");        //print job list        System.out.println(s);    }}

public class Main {    public static void main(String[] args) {        HeadHunter hh = new HeadHunter();        hh.registerObserver(new JobSeeker("Mike"));        hh.registerObserver(new JobSeeker("Chris"));        hh.registerObserver(new JobSeeker("Jeff"));         //每次添加一个个job，所有找工作人都可以得到通知。        hh.addJob("Google Job");        hh.addJob("Yahoo Job");    }}

//抽象观察者角色public interface Watcher{    public void update(String str);}

//抽象主题角色，watched：被观察public interface Watched{    public void addWatcher(Watcher watcher);    public void removeWatcher(Watcher watcher);    public void notifyWatchers(String str);}

public class ConcreteWatcher implements Watcher{    @Override    public void update(String str)    {        System.out.println(str);    }}

import java.util.ArrayList;import java.util.List;public class ConcreteWatched implements Watched{    // 存放观察者private List
    
      list = new ArrayList
     
      ();    @Override    public void addWatcher(Watcher watcher)    {        list.add(watcher);    }    @Override    public void removeWatcher(Watcher watcher)    {        list.remove(watcher);    }    @Override    public void notifyWatchers(String str)    {        // 自动调用实际上是主题进行调用的for (Watcher watcher : list)        {            watcher.update(str);        }    }}
     
    

public class Test{    public static void main(String[] args)    {        Watched girl = new ConcreteWatched();                Watcher watcher1 = new ConcreteWatcher();        Watcher watcher2 = new ConcreteWatcher();        Watcher watcher3 = new ConcreteWatcher();                girl.addWatcher(watcher1);        girl.addWatcher(watcher2);        girl.addWatcher(watcher3);                girl.notifyWatchers("开心");    }}

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 entityclass 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;    }}

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