Command Method

It encapsulates a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations. This pattern decouples the sender of a request from its receiver, allowing for better flexibility and control over the execution of requests.

Structure

• Command Interface: Declares a method for executing a command.
• Concrete Command: Implements the command interface and defines the binding between a receiver and an action.
• Receiver: Knows how to perform the operations associated with the command.
• Invoker: Asks the command to execute the request.
• Client: Creates the command and associates it with a receiver.

Example

// Command Interface
interface Command {
    void execute();
}

// Concrete Command for turning on the light
class LightOnCommand implements Command {
    private Light light;

    public LightOnCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.turnOn();
    }
}

// Concrete Command for turning off the light
class LightOffCommand implements Command {
    private Light light;

    public LightOffCommand(Light light) {
        this.light = light;
    }

    @Override
    public void execute() {
        light.turnOff();
    }
}

// Receiver class
class Light {
    public void turnOn() {
        System.out.println("Light is ON");
    }

    public void turnOff() {
        System.out.println("Light is OFF");
    }
}

// Invoker class
class RemoteControl {
    private Command command;

    public void setCommand(Command command) {
        this.command = command;
    }

    public void pressButton() {
        command.execute();
    }
}

// Client code
public class Main {
    public static void main(String[] args) {
        Light livingRoomLight = new Light();

        // Create Command Objects
        Command lightOn = new LightOnCommand(livingRoomLight);
        Command lightOff = new LightOffCommand(livingRoomLight);

        // Create Invoker
        RemoteControl remote = new RemoteControl();

        // Turn the light ON
        remote.setCommand(lightOn);
        remote.pressButton();  // Output: Light is ON

        // Turn the light OFF
        remote.setCommand(lightOff);
        remote.pressButton();  // Output: Light is OFF
    }
}