package designpatterns.observer.java;public interface Subject {        /**     * Attaches an <i>Observer</i> to this <i>Subject</i>.     */    public void addObserver(Observer o);    /**     * Detaches an <i>Observer</i> from this <i>Subject</i>.     */    public void removeObserver(Observer o);    /**     * Notifies all <i>Observer</i>s.     */    public void notifyObservers();}