Behavioral design patterns define how objects communicate and interact. They clarify responsibilities between components and streamline communication, making code easier to extend and maintain.

The Observer Pattern

This pattern sets up a one-to-many dependency, so when one object changes state, all dependents are notified automatically. It's useful when changes in one object should trigger updates in others. For example, a notification system updating multiple components when a new message arrives.

The Strategy Pattern

It defines a family of algorithms, encapsulates them, and makes them interchangeable. It’s useful when behavior must change at runtime. For example, a sorting system choosing different algorithms based on data size or format.

The Command Pattern

Turns requests into objects, enabling them to be queued, logged, or undone. It’s common in GUIs and transactional systems. For example, a text editor where Cut, Copy, and Paste are encapsulated with undo/redo support.

The Iterator Pattern

This pattern provides a way to traverse a collection without exposing its internal representation. It's useful for lists, trees, or complex structures, keeping iteration logic separate from the data structure itself.

These patterns enhance flexibility and communication between components by separating concerns and defining reusable interaction strategies.