State pattern example

Definition: The Observer Pattern defines a one to many dependency between objects so that one object changes state, all of its dependents are notified and updated automatically . Explanation: One to many dependency is between Subject(One) and Observer(Many).

The observer design pattern is used when a list of objects needs to be notified about a change that they are observing .

Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its depenedent objects are to be notified automatically . Observer pattern falls under behavioral pattern category.