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


class Towar implements Observer {

    private double pricePLN;
    private double priceEUR;



    @Override
    public void update() {
        pricePLN = priceEUR * nbp.getKurs();
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

interface Observer {
    public abstract void update();}
}

class Calculate extends Observer {

    public Calculate(Towar towar) {
        this.towar = towar;
        this.towar.attach(this);
    }

    @Override
    public void update() {

        System.out.println("Cena w PLN: " + towar.getState());
    }
}

class NBP {

    private List<Observer> observers = new ArrayList<Observer>();

    private double kurs = 4.2;

    public double getKurs() {
        return kurs;
    }

    public void changeKurs(double kurs) {
        this.kurs = kurs;
        notifyAllObservers();
    }

    public void attach(Observer observer) {
        observers.add(observer);
    }

    public void notifyAllObservers() {
        for (Observer observer : observers) {
            observer.update();
        }
    }

}

public class Sklep {

    public static void main(String[] args) {
        // TODO code application logic here
        Towar towar = new Towar();

        new Calculate(towar);

        System.out.println("cena w euro: 15");
        towar.setState(20);
        System.out.println("cena w euro: 10");
        towar.setState(10);
    }
}