package class5_1_Observer;

import java.util.HashSet;
import java.util.Set;

public abstract class PositionSubject {
    private Set<Observer> observers = new HashSet<Observer>();

    public void addObserver(Observer o) {
        observers.add(o); // Because observer is a set, it
        // will only add if the observer is not already there.
    }

    public void removeObserver(Observer o) {
        observers.remove(o);
        // will not throw error if o is not already in the set.
    }

    /**
     * This method should be called once per
     * simulated second by the concrete subject.
     * @param position distance from start
     */
    public void notifyObservers(double position) {
        for(Observer o: observers) {
            o.update(position);
        }
    }
}