Observer

package Patterns.Behavioral.observer;

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

public class YouTubeChannelSubject{
    private String channelName;
    private List<String> contents;
    List<Observer> subscriberObservers;
    public YouTubeChannelSubject(){
        this.channelName = "Mr.Beast";
        contents = new ArrayList<>();
        subscriberObservers = new ArrayList<>();
    }
    public void addNewContent(String name){
        contents.add(name);
        //notify all listeners
        notifySubscriberObserver();
    }
    public void removeContent(String name){
        if(contents.contains(name)){
            contents.remove(name);
            //notify all listeners
            notifySubscriberObserver();
        }
    }
    public List<String> getContents(){
        return this.contents;
    }
    public String getChannelName(){
        return this.channelName;
    }
    public void addObserver(Observer observer){
        this.subscriberObservers.add(observer);
    }

    public void removeObserver(Observer observer){
        this.subscriberObservers.remove(observer);
    }

    public void notifySubscriberObserver(){
        for(Observer subscriber : subscriberObservers){
            subscriber.update();
        }
    }

}

package Patterns.Behavioral.observer;

public abstract class Observer {
    public String subscriberName;
    public YouTubeChannelSubject subject;
    public Observer(YouTubeChannelSubject youTubeChannelSubject,String name){
        this.subject = youTubeChannelSubject;
        this.subscriberName = name;
    }
    abstract void update();
    public YouTubeChannelSubject getSubject(){
        return this.subject;
    }
}

package Patterns.Behavioral.observer;

public class SubscriberOneObserver extends Observer {
    public SubscriberOneObserver(YouTubeChannelSubject subject,String name){
        super(subject,name);
        // add this subscriber as of the observers of the youtube channel defined by object 'subject'
        this.subject.addObserver(this);
    }

    @Override
    void update() {
        System.out.println(this.subscriberName +" got updated !");
        System.out.println(this.subject.getChannelName()+" has updated contents, the total content on the channel now is "+ this.subject.getContents().size());
        System.out.println("List of contents on the channel "+this.subject.getChannelName()+" are  as follows: ");
        for(String content : subject.getContents()){
            System.out.println(content);
        }
        System.out.println("------------------------------");
    }

}

package Patterns.Behavioral.observer;

public class SubscriberTwoObserver extends Observer {
    public SubscriberTwoObserver(YouTubeChannelSubject subject,String name){
        super(subject,name);
        // add this subscriber as of the observers of the youtube channel defined by object 'subject'
        this.subject.addObserver(this);
    }

    @Override
    void update() {
        System.out.println(this.subscriberName +" got updated !");
        System.out.println(this.subject.getChannelName()+" has updated contents, the total content on the channel now is "+ this.subject.getContents().size());
        System.out.println("List of contents on the channel "+this.subject.getChannelName()+" are  as follows: ");
        for(String content : subject.getContents()){
            System.out.println(content);
        }
        System.out.println("------------------------------");
    }

}

package Patterns.Behavioral.observer;

public class Main {
    public static void main(String args[]){
        //creating youtube channel
        YouTubeChannelSubject subject = new YouTubeChannelSubject();

        //subscriber's of the above youtube channel
       new SubscriberOneObserver(subject,"prashant");
       new SubscriberTwoObserver(subject,"sandeep");

       //now updating the contents of the youtube channel
       subject.addNewContent("Men Vs Women survive the wilderness of $500,000");
       subject.addNewContent("7 Days stranded in a cave");
    }
}

prashant got updated !
Mr.Beast has updated contents, the total content on the channel now is 1
List of contents on the channel Mr.Beast are  as follows: 
Men Vs Women survive the wilderness of $500,000
------------------------------
sandeep got updated !
Mr.Beast has updated contents, the total content on the channel now is 1
List of contents on the channel Mr.Beast are  as follows: 
Men Vs Women survive the wilderness of $500,000
------------------------------
prashant got updated !
Mr.Beast has updated contents, the total content on the channel now is 2
List of contents on the channel Mr.Beast are  as follows: 
Men Vs Women survive the wilderness of $500,000
7 Days stranded in a cave
------------------------------
sandeep got updated !
Mr.Beast has updated contents, the total content on the channel now is 2
List of contents on the channel Mr.Beast are  as follows: 
Men Vs Women survive the wilderness of $500,000
7 Days stranded in a cave
------------------------------
prashantmishra@Prashants-MacBook-Air machinecoding %