command

Command Pattern

The Command Pattern is a behavioral design pattern that encapsulates a request as an object, thereby allowing you to parameterize objects with requests, delay their execution, or support undoable operations.

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📖 What is the Command Pattern?

The Command Pattern encapsulates a request as an object. It separates the object that invokes the operation from the one that knows how to perform it.

Key features:

1. Encapsulation: Encapsulates a request as an object.
2. Decoupling: Decouples the invoker and the receiver.
3. Undo/Redo: Provides support for undoable operations.

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🔧 Implementation

The implementation of the Command Pattern can be found in:

• Command.java: The interface for all commands.
• Light.java: The receiver class.
• LightOnCommand.java, LightOffCommand.java: Concrete command implementations.
• RemoteControl.java: The invoker class.
• Main.java: Demonstrates the usage of the Command Pattern.

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🛠️ Example Usage

To see the Command Pattern in action, refer to the Main.java file. It demonstrates controlling a light using commands.

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📊 UML Diagram

classDiagram
direction LR
    class Client {
    }

    class Invoker {
    }

    class Command {
        +Execute()
    }

    class ConcreteCommand {
        -state
        +Execute()
    }

    class Receiver {
        +Action()
    }

    Client --> Invoker
    Invoker o--> Command
    Command <|-- ConcreteCommand
    ConcreteCommand --> Receiver : receiver
    Client --> Receiver
    Client --> ConcreteCommand

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Note

If the UML above is not rendering correctly, you can view the diagram from the command_uml.png file.

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📝 Key Takeaways

• The Command Pattern encapsulates a request as an object, allowing you to parameterize objects with requests.
• It decouples the invoker from the receiver, providing support for undoable operations.
• Use it when you need to support operations such as undo, redo, or queuing requests.