This chapter covers the observer pattern.
GoF Definition
Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
Concept
In this pattern, there are many observers (objects) that are observing a particular subject (also an object). Observers register themselves to a subject to get a notification when there is a change made inside that subject. When they lose interest of the subject, they simply unregister from the subject. It is also referred to as the publish-subscribe pattern . The whole idea ...
