The Observer Pattern is a behavioral design pattern that allows an object, called the subject, to maintain a list of its dependents, called observers, and notify them automatically of any state changes. This pattern promotes loose coupling between the subject and observers, enabling the subject to be easily extended and reused without modifying the observers.
In the Observer Pattern, the subject and observers interact through predefined interfaces. The subject provides a way for observers to register or unregister themselves, while the observers provide handlers to be notified when a state change occurs. When the subject's state changes, it notifies all the registered observers by calling their update methods, typically passing information about the change as an argument.
The Observer Pattern is commonly used in event-driven systems, user interfaces, and distributed systems. It allows for a decoupled and flexible architecture, where multiple observers can react independently to changes in the subject, without the need for direct dependencies between them.