Behavioral Design Patterns
Behavioral design patterns are a group of design patterns that focus on how objects interact and communicate with each other. They manage the flow of control and responsibilities in an application, promoting loose coupling and flexibility in system design. Behavioral patterns provide solutions to common communication and collaboration problems among objects.
There are 11 well-known behavioral design patterns:
1. Chain of Responsibility Pattern:
The Chain of Responsibility pattern passes a request along a chain of handlers until one of them handles the request. It decouples the sender and receiver of a request, allowing multiple objects to handle the request without explicitly knowing which one will process it.
Example:
Implementing a logging system with multiple logging levels (e.g., info, warning, error) where each logger can decide to handle the log or pass it to the next logger.
2. Command Pattern:
The Command pattern encapsulates a request as an object, allowing parameterization of clients with different requests, queuing of requests, and logging of their execution. It enables loose coupling between the sender and receiver of a command.
Example:
Creating an undo/redo functionality in a text editor by representing each editing action as a command object.
3. Interpreter Pattern:
The Interpreter pattern provides a way to evaluate language grammar or expressions. It is used to interpret and execute domain-specific languages (DSLs).
Example:
Implementing a calculator that can interpret and evaluate mathematical expressions in postfix notation.
4. Iterator Pattern:
The Iterator pattern provides a way to access elements of a collection sequentially without exposing its underlying representation. It allows traversal through a collection without the need to know its internal structure.
Example:
Iterating through a list of items without exposing the list’s implementation details.
5. Mediator Pattern:
The Mediator pattern defines an object that encapsulates communication between objects in a system, reducing their direct interactions and dependencies. It promotes the principle of “centralized control” to manage complex interactions.
Example:
Creating a chat application where the mediator manages communication between users and handles message broadcasting.
6. Memento Pattern:
The Memento pattern allows an object’s state to be captured and restored later without exposing its internal structure. It enables undo/redo and snapshot functionality.
Example:
Implementing a text editor with undo and redo capabilities by using memento objects to store and restore the editor’s state.
7. Observer Pattern:
The Observer pattern defines a one-to-many dependency between objects, so when one object changes state, its dependents (observers) are notified and updated automatically.
Example:
Creating a stock market monitoring system where multiple clients (observers) receive real-time updates on stock prices when they change.
8. State Pattern:
The State pattern allows an object to change its behavior when its internal state changes. It encapsulates state-specific logic in separate classes, making it easier to manage and extend.
Example:
Implementing a traffic light system with different states (e.g., green, yellow, red), and each state determines the next state transition.
9. Strategy Pattern:
The Strategy pattern defines a family of algorithms and makes them interchangeable. It allows clients to choose the algorithm they need without modifying the client code.
Example:
Implementing different sorting algorithms (e.g., bubble sort, merge sort) as strategies that can be easily switched based on the user’s preference.
10. Template Method Pattern:
The Template Method pattern defines the structure of an algorithm in a method but allows its subclasses to override certain steps of the algorithm. It promotes code reusability and follows the “Hollywood Principle” (“Don’t call us, we’ll call you”).
Example:
Creating a game framework where a game developer can extend and customize the game’s behavior by providing their implementations of specific methods.
11. Visitor Pattern:
The Visitor pattern lets you add further operations to objects without having to modify them. It separates the operations into visitor objects, allowing new operations to be added easily.
Example:
Implementing a document processing system where different visitors can perform various actions on elements of the document (e.g., rendering, exporting, analyzing).
Each of these behavioral design patterns provides a solution to specific interaction and communication challenges in software design. By understanding and applying these patterns, developers can create more flexible, maintainable, and extensible software systems.