© Vaskaran Sarcar 2019
Vaskaran SarcarJava Design Patternshttps://doi.org/10.1007/978-1-4842-4078-6_14

14. Observer Pattern

Vaskaran Sarcar1 
Bangalore, Karnataka, India

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.


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 ...

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