Java Design Patterns: A Hands-On Experience with Real-World Examples

© The Author(s), under exclusive license to APress Media, LLC, part of Springer Nature 2022

V. SarcarJava Design Patternshttps://doi.org/10.1007/978-1-4842-7971-7_16

16. Observer Pattern

Vaskaran Sarcar¹  

(1)

Garia, Kolkata, India

 

This chapter covers the Observer pattern.

GoF Definition

It defines 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 two types of objects. One is an observer and the other is the subject. What is an observer? In simple words, it is an object that needs to be informed when interesting stuff happens in another object. The object about whom an observer is interested is called the subject.

Normally many observers ...