ObserverPattern

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

public class ObserverPattern {

    public static void main(String[] args){
        WayneIndustries wayneIndustries = new WayneIndustries();
        wayneIndustries.subscribeObserver(new Superhero("Batman"));
        wayneIndustries.subscribeObserver(new Superhero("Robin"));

        wayneIndustries.addWeapon("Batarang");
        wayneIndustries.addWeapon("Batman's utility belt");
    }

}

interface Subject {
    void subscribeObserver(Observer observer);
    void unsubscribeObserver(Observer observer);
    void notifyAllObserver();
}

interface Observer {
    void update(Subject subject);
}

class WayneIndustries implements Subject {

    List<Observer> observerList;
    List<String> weaponsList;

    WayneIndustries(){
        observerList = new ArrayList<Observer>();
        weaponsList = new ArrayList<String>();
    }

    public void subscribeObserver(Observer observer) {
        observerList.add(observer);
    }

    public void unsubscribeObserver(Observer observer) {
        observerList.remove(observer);
    }

    public void notifyAllObserver() {
        for(Observer observer: observerList){
            observer.update(this);
        }
    }

    public void addWeapon(String weapon){
        weaponsList.add(weapon);
        notifyAllObserver();
    }

    public List<String> getWeapon(){
        return weaponsList;
    }

    public String toString(){
        return weaponsList.toString();
    }
}

class Superhero implements Observer {
    private String name;

    Superhero(String name){
        this.name = name;
    }

    public void update(Subject subject) {
        System.out.println(this.name + " got notified");
        System.out.println(subject);
    }
}