PublisherSubscriber

/*
 * Click nbfs://nbhost/SystemFileSystem/Templates/Licenses/license-default.txt to change this license
 */
//https://medium.com/@smagid_allThings/uml-class-diagrams-tutorial-step-by-step-520fd83b300b
package com.mycompany.publishsubscribe;

import java.util.*;

/**
 *
 * @author IvoRakitin
 */
public class PublishSubscribe {

    public static void main(String[] args) {

        Publisher publisher = new Publisher("p1");
        Subscriber s1 = new Subscriber("s1");
        s1.subscribe(publisher);
        Subscriber s2 = new Subscriber("s2");
        s2.subscribe(publisher);
        Subscriber s3 = new Subscriber("s3");
        s3.subscribe(publisher);
        publisher.doWork();
        s2.unsubscribe(publisher);
        System.out.println();
        publisher.doWork();
        /*
        int numSubs = 10;
        Publisher p1 = new Publisher("p1");
        Publisher p2 = new Publisher("p2");
        Subscriber[] s = new Subscriber[numSubs];
        for (int i = 0; i < s.length; i++) {
            s[i] = new Subscriber("s" + i);
            s[i].subscribe(p1);
            if (i % 2 == 0)
                s[i].subscribe(p2);
        }
        p1.doWork();
        p2.doWork();
        for (int i = 0; i < s.length; i++) {
            if (i % 2 != 0)
                s[i].unsubscribe(p1);
        }
        System.out.println("");
        p1.doWork();
        p2.doWork();   */
    }
}

class Publisher {

    private List<Calling> subscribers;
    private String name;

    public Publisher(String name) {
        subscribers = new ArrayList<>();
        this.name = name;
    }

    public interface Calling {
        public void call(Object state, String n);
    }

    public void subscribe(Calling sub) {
        subscribers.add(sub);
    }

    public void unsubscribe(Calling subscriber) {
        subscribers.remove(subscriber);
    }

    public void doWork() {
        for (int i = 0; i < 100; i++) {
            if (i == 50) {
                for (Calling subscriber : subscribers) {
                    subscriber.call(i, name);
                }
            }
        }
    }
}

class Subscriber {

    private String name;
    private Publisher.Calling calling;

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

    public void subscribe(Publisher publisher) {
        if (calling == null) {

            /*
            calling = (Object state) -> {
                stateChanged(state);
            };*/
            calling = new Publisher.Calling() {
                @Override
                public void call(Object state, String n) {
                    stateChanged(state, n);
                }
            };
        }
        publisher.subscribe(calling);
    }
    public void unsubscribe(Publisher publisher) {
        if (calling != null) {
            publisher.unsubscribe(calling);
        }
    }
    private void stateChanged(Object state, String n) {
        System.out.println("Subscriber " + name + " called with state " + state + " from Publisher " + n);
    }
}