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Command Design Pattern
4 min readApr 10, 2019
The Command pattern is a behavioural design pattern, in which an abstraction exists between an object that invokes a command, and the object that performs it.
E.g., a button will call the Invoker, that will call a pre-registered Command, that the Receiver will perform.
A Concrete Class will delegate a request to a command object, instead of implementing the request directly.
Using a command design pattern allows you to separate concerns and to solve problems of the concerns independently of each other.
E.g., logging the execution of a command and its outcome.
The command pattern is a good solution for implementing UNDO/REDO functionality into your application.
Uses:
- GUI Buttons, menus
- Macro recording
- Multi-level undo/redo
- Networking — send whole command objects across a network, even as a batch
- Parallel processing or thread pools
- Transactional behaviour
- Wizards
Terminology
- Receiver: The object that will receive and execute the command.
- Invoker: The object that sends the command to the receiver. E.g., A button.
- Command Object: Itself, an object, that implements an execute, or action method, and contains all required information to execute it.
