Design Patterns
Command Pattern
The Command Pattern is a behavioral design pattern that encapsulates a request as an object, thereby allowing parameterization of clients with different requests, queuing of requests, and logging of requests. It also supports undoable operations.
Usage Scenarios
- Menu Systems: Commands can represent menu items, where each command knows how to execute a specific action when the menu item is selected.
- Undo Mechanisms: Commands can store enough information to undo their actions, providing a robust undo functionality.
- Multi-Level Undo: By maintaining a history of executed commands, it becomes possible to undo multiple levels of operations sequentially.
- Transactional Behavior: Commands can be used to encapsulate a series of actions that must either all succeed or all fail (similar to database transactions).
Key Concepts
- Encapsulation: Commands encapsulate all the details of an operation (action and receiver) into an object, making them standalone and reusable.
- Decoupling: It decouples the sender (client that initiates a request) from the receiver (object that performs the actual action), allowing changes in one without affecting the other.
- Flexibility: Commands can be stored, queued, and undone. This is useful for implementing features like undo-redo functionality or transactional behavior.
General Tips!
- Identify Common Problems: Recognize recurring problems in your code to determine which design pattern can provide a solution.
- Understand the Principles: Familiarize yourself with SOLID principles as they often align with the motivations behind design patterns.
- Use Patterns Judiciously: Avoid overusing patterns; apply them only when they provide a clear benefit.
- Learn by Example: Study real-world examples of design patterns to see how they are implemented in practice.
- Refactor When Necessary: Don’t force a pattern from the start; refactor your code to introduce patterns when a need becomes apparent.
- Stay Flexible: Patterns are guidelines, not strict rules. Adapt them to fit your specific context.
- Document Your Design: Clearly document the use of design patterns to help future maintainers understand your design decisions.