Observer mode

Observer mode ： Define one to many dependencies between objects , So when an object changes state , All objects that depend on him will be notified .

apply ： When an event triggers , Or a state changes , Many corresponding places need corresponding changes , It can avoid excessive resource consumption caused by polling .

I thought of a beep beep Examples of video numbers being subscribed , Both video numbers and subscribers can be expanded

Source code

package  Design patterns . Notifier mode ;

public class main {
    // Example ideas 
    // b standing   There's a video number   , You can subscribe to the video number , And the video Number update can receive the notification of the video number 

    public static void main(String[] args) {
        BiliBili b = new BiliBili();
        b.setVideo(new VideoNo(" Video Number 1"));
        b.setVideo(new VideoNo(" Video Number 2"));

        UserObserver userObserver1 = new UserObserver(" user 1");
        UserObserver userObserver2 = new UserObserver(" user 2");

        // user 1 Subscribe to a video number 1
        userObserver1.addVideo(b.getVideo(" Video Number 1"));
        // user 1 Subscribe to a video number 2
        userObserver1.addVideo(b.getVideo(" Video Number 2"));
        // user 2 Subscribe to a video number 1
        userObserver2.addVideo(b.getVideo(" Video Number 1"));

        // Video Number update 
        b.getVideo(" Video Number 1").upData(" Video Number 1 Updated joke video ");
        b.getVideo(" Video Number 2").upData(" Video Number 2 Updated eating and broadcasting video ");

        // Both video numbers and users can be added dynamically 

    }

}


package  Design patterns . Notifier mode ;

import sun.jvm.hotspot.opto.HaltNode;

import java.util.HashMap;
import java.util.Map;

public class BiliBili {
    //B Stack all video numbers 
    Map<String,Video> videoMap = new HashMap<>();
    // Get a video number 
    public Video getVideo(String videoName){
        return videoMap.get(videoName);
    }
    // Put in a video number 
    public void setVideo(Video video){
         videoMap.put(video.getVideoName(),video);
    }
}
package  Design patterns . Notifier mode ;

public interface Observer {
    // Subscribe to a video number 
    void addVideo(Video v);
    // Delete and subscribe to a video number 
    void delVideo(Video v);
    // Accept notice 
    void printData(String data);
    // Return the subscriber name 
    String getName();
}

package  Design patterns . Notifier mode ;

/**
 *  Video number class 
 */
public interface Video {
    // Add subscribers 
    void addUser(Observer user);
    // Reduce the number of subscribers 
    void delUser(Observer user);
    // Update the video 
    void upData(String data);
    // Get the name of the video number 
    String getVideoName();
}

package  Design patterns . Notifier mode ;

import java.util.HashMap;
import java.util.Map;

public class UserObserver implements Observer {

    // Subscribe to the video list 
    Map<String,Video> videoMap;
    // Subscriber name 
    String userName;

    public UserObserver(String userName) {
        this.userName = userName;
        videoMap = new HashMap<>();
    }

    @Override
    public void addVideo(Video v) {
        v.addUser(this);
        videoMap.put(v.getVideoName(),v);
    }

    @Override
    public void delVideo(Video v) {
        v.delUser(this);
        videoMap.remove(v.getVideoName());
    }

    @Override
    public void printData(String data) {
        System.out.println(" Subscribe to the people "+userName+" Message received ："+data);
    }

    @Override
    public String getName() {
        return userName;
    }
}

package  Design patterns . Notifier mode ;

import java.util.HashMap;
import java.util.Map;

public class VideoNo implements Video{

    // Subscribers who need to be notified 
    Map<String,Observer> observerMap;
    // Name of video Number 
    String name;

    public VideoNo(String name) {
        this.name = name;
        this.observerMap = new HashMap<>();
    }

    @Override
    public void addUser(Observer user) {
        observerMap.put(user.getName(),user);
    }

    @Override
    public void delUser(Observer user) {
        observerMap.remove(user.getName());
    }

    @Override
    public void upData(String data) {
        for (Observer value : observerMap.values()) {
           value.printData(data);
        }
    }

    @Override
    public String getVideoName() {
        return name;
    }
}