Changes

<b>Subject</b>: Knows its observers and provides an interface for attaching and detaching observers

<b>Observer</b>: Defines an updating interface for objects that should be notified

<b>ConcreteSubject</b>: Stores states of ConcreteObservers objects. Sends a notification when a change has occurred

<b>ConcreteObserver</b>: Maintains a reference to the ConcreteSubjects object. Synchronizes itself with the ConcreteSubject's state.