package class4_1_Observer_start; // MSOE. Dr. Yoder. 04 January 2016.

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

public abstract class LinearSubject {
    protected double positionMeters = 0;

    private Set<PositionObserver> observers = new HashSet<PositionObserver>();

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

    public void removeObserver(PositionObserver 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.
     * (This is to make the example simpler. In practice, a timestamp should probably be included
     * with the subject.)
     */
    public void notifyObservers() {
        for(PositionObserver o: observers) {
            o.update(positionMeters);
        }
    }
}