Key components of the Command Pattern

1. Command Interface or Abstract Class

This is an interface or abstract class that declares an execute method, defining the contract for concrete commands. It ensures that all commands have a method to perform their actions.

2. Concrete Command

Concrete command classes implement the Command interface or inherit from the abstract class. Each concrete command encapsulates a specific action to be performed. For instance, you might have concrete commands to turn on lights, open files, or send messages.

3. Receiver

The receiver is responsible for performing the actual work when a command is executed. It knows how to carry out the requested action. For example, in a home automation system, the receiver could be a “Light” object that understands how to turn on and off.

4. Invoker

The invoker is responsible for triggering the execution of commands. It holds references to the commands and can execute them. It acts as an intermediary between the sender (client) and the receiver, ensuring that the sender remains decoupled from the receiver.

The Command Pattern is a behavioral design pattern that focuses on encapsulating a request as an object, thereby decoupling the sender of the request from the receiver. This pattern allows you to parameterize objects with commands, delay or queue a request’s execution, and support undoable operations. It’s a fundamental pattern for implementing a wide range of functionality in software systems.