Changes

== Structure ==

Subject: Knows its observers and provides an interface for attaching and detaching observers

Observer: Defines an updating interface for objects that should be notified

ConcreteSubject: Stores states of ConcreteObservers objects. Sends a notification when a change has occurred

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