Observer Pattern

• Observer Pattern is one of the pattern often used in JDK.
• 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.
• Observer pattern uses three actor classes. Subject, Observer and Client. Subject is an object having methods to attach and detach observers to a client object. We have created an abstract class Observer and a concrete class Subject that is extending class Observer.

Reference

• tutorialspoint:Observer
• journaldev:Observer
• geeksforgeeks:Observer
• iluwatar:Observer