What is the purpose of using an observer?

Observable is used to create subclasses that other parts of the program can observe . When an object of such subclass undergoes a change, observing classes are notified. The update( ) method is called when an observer is notified of a change.

The observer method is a Behavioral design Pattern which allows you to define or create a subscription mechanism to send the notification to the multiple objects about any new event that happens to the object that they are observing . The subject is basically observed by multiple objects.

The responsibility of observers is to register (and unregister) themselves on a subject (to get notified of state changes) and to update their state (synchronize their state with the subject’s state) when they are notified.