CODESAMPLE

Command - Java

Command Java

The Command pattern encapsulates a request as an object, thereby allowing for parameterization of clients with different requests, queuing or logging of requests, and support for undoable operations. This implementation defines a Command interface with an execute method. Concrete commands like TurnOnCommand and TurnOffCommand implement this interface, holding a reference to the Light (the receiver). The RemoteControl acts as the invoker, accepting and executing commands. This aligns with Java’s OOP principles promoting loose coupling and extensibility. Using interfaces and concrete classes is a standard Java approach for achieving polymorphism and a clean design.

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

// Receiver
class Light {
    private boolean on;

    public void turnOn() {
        on = true;
        System.out.println("Light is on");
    }

    public void turnOff() {
        on = false;
        System.out.println("Light is off");
    }

    public boolean isOn() {
        return on;
    }
}

// Concrete Commands
class TurnOnCommand implements Command {
    private final Light light;

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

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

class TurnOffCommand implements Command {
    private final Light light;

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

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


// Invoker
class RemoteControl {
    private Command slot;

    public RemoteControl() {
    }

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

    public void buttonPressed() {
        slot.execute();
    }
}

// Main
public class CommandExample {
    public static void main(String[] args) {
        Light light = new Light();
        TurnOnCommand turnOn = new TurnOnCommand(light);
        TurnOffCommand turnOff = new TurnOffCommand(light);

        RemoteControl remote = new RemoteControl();
        remote.setCommand(turnOn);
        remote.buttonPressed(); // Light is on

        remote.setCommand(turnOff);
        remote.buttonPressed(); // Light is off
    }
}