观察者设计模式

MessageSubject接口(被观察者接口)

package observer;

//被观察者接口
public interface MessageSubject {
    //添加观察者
    public void addObserver(Observer observer);
    //移除观察者
    public void removeObserver(Observer observer);
    //通知所有观察者
    public void notifyObservers();
}

Observer接口(观察者接口)

package observer;

public interface Observer {
    //更新
    public void update(String str);
}

Message类(被观察者实现类)

package observer;

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

public class Message implements MessageSubject {
    private String msg;
    //维护的观察者列表
    private List<Observer> list=new ArrayList<>();

    public void sendMsg(String str){
        msg=str;
        notifyObservers();
    }

    @Override
    public void addObserver(Observer observer) {
        list.add(observer);
    }

    @Override
    public void removeObserver(Observer observer) {
        list.remove(observer);
    }

    @Override
    public void notifyObservers() {
        for(Observer observer:list){
            observer.update(msg);
        }
    }
}

User类(观察者实现类)

package observer;

public class User implements Observer {
    private String name;

    public User(String name) {
        this.name = name;
    }

    @Override
    public void update(String str) {
        System.out.println("["+name+"]"+"收到消息:"+str);
    }
}

测试

package observer;

public class ObserverTest {
    public static void main(String[] args) {
        User user1=new User("tom");
        User user2 = new User("lily");

        Message message = new Message();
        message.addObserver(user1);
        message.addObserver(user2);
        message.sendMsg("hello......");
    }
}

结果

"C:\Program Files\Java\jdk-9.0.4\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\idea_rt.jar=53587:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\bin" -Dfile.encoding=UTF-8 -classpath "D:\java\test\bin;D:\java\test\libs\guava-27.0-jre.jar;D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\junit.jar;D:\java\test\libs\apache-mina-2.0.20\dist\mina-core-2.0.20.jar;D:\java\test\libs\apache-mina-2.0.20\lib\slf4j-api-1.7.26.jar;D:\java\test\libs\jdom-2.0.6.jar;D:\java\test\libs\dom4j-2.0.2.jar;D:\java\test\libs\xstream-1.4.11.1.jar;D:\java\test\libs\xpp3-1.1.3.4.C.jar;D:\java\test\libs\gson-2.8.4.jar" observer.ObserverTest
[tom]收到消息:hello......
[lily]收到消息:hello......