Observer pattern

import java.util.*;

interface StockObservable{
    public void addObserver(Observer obj);
    public void removeObserver(Observer obj);
    public void notifyObservers();
    public void setData(int newStock);
    public int getData();
}


class IphoneObservable implements StockObservable{
    List<Observer> observers = new ArrayList<>();
    int currentStock = 0;
    public void addObserver(Observer obj){
        this.observers.add(obj);
    }
    public void removeObserver(Observer obj){
        this.observers.remove(obj);
    }
    public void notifyObservers(){
        for(Observer obj: this.observers){
            obj.update();
        }
    }
    public void setData(int newStock){
        if(this.currentStock != newStock){
            notifyObservers();
            currentStock = newStock;
        }
    }
    public int getData(){
        return currentStock;
    }
}

interface Observer{
    public void update();
}

class MobileObserver implements Observer{

    StockObservable observable;
    String username;

    MobileObserver(String username, StockObservable observable){
        this.username = username;
        this.observable = observable;
    }

    public void update(){
        System.out.println("mssg sent to" + this.username);
    }
}


public class Main{
    public static void main(String args[]){
        StockObservable iphones = new IphoneObservable();

        Observer observer1 = new MobileObserver("anon", iphones);
        Observer observer2 = new MobileObserver("anon2", iphones);

        iphones.addObserver(observer1);
        iphones.addObserver(observer2);

        iphones.setData(100);

    }
}