title: Why do I need to call setChanged before I notify the observers?
body: <p>I've recently read about Java's <a href="http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Observable.html#setChanged%28%29" rel="noreferrer">Observable</a> class. What I don't understand is this: before notifying the observers (notifyObservers()) I must call setChanged(). There is a boolean inside notifyObservers method that requires us to call setChanged. What is the purpose of the boolean value and why must I call setChanged()?</p>