The Observer Pattern is a behavioral design pattern that establishes a one-to-many relationship between objects. When one object (the subject) changes state, all its dependents (observers) are notified and updated automatically¹. This pattern is particularly useful for implementing distributed event-handling systems and is a crucial part of many software architectures, including Model-View-Controller (MVC)³.

Key Components

1. Subject: Maintains a list of observers and provides methods to register, unregister, and notify them of changes.

2. Observer: Defines an interface with an update method that concrete observers must implement.

3. ConcreteSubject: A specific implementation of the subject that holds the actual state or data.

4. ConcreteObserver: Implements the observer interface and reacts to changes in the subject’s state¹.

Example Implementation

Consider a weather monitoring system where different parts of your application need to be updated when the weather conditions change.