Observer Pattern Tutorial

Introduction

The Observer Pattern is one of the behavioral design patterns. It defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. This pattern is commonly used in event-driven systems, where the change in one object needs to be reflected across multiple dependent objects.

Components of the Observer Pattern

The Observer Pattern consists of the following components:

• Subject: The object that holds the state and notifies observers of changes to its state.
• Observer: The object that gets notified of changes in the Subject.
• Concrete Subject: A concrete implementation of the Subject that maintains a list of observers and sends notifications.
• Concrete Observer: A concrete implementation of the Observer that updates its state when notified by the Subject.

UML Diagram

The UML diagram of the Observer Pattern is shown below: