Command

from: Command Pattern Tutorial with Java Examples

Example

Command

public interface Command {

    public void execute();

}

public class LunchCommand implements Command {

    Lunch lunch;

    public LunchCommand(Lunch lunch) {
        this.lunch = lunch;
    }

    @Override
    public void execute() {
        lunch.makeLunch();
    }

}

public class DinnerCommand implements Command {

    Dinner dinner;

    public DinnerCommand(Dinner dinner) {
        this.dinner = dinner;
    }

    @Override
    public void execute() {
        dinner.makeDinner();
    }

}

Receiver

public class Lunch {

    public void makeLunch() {
        System.out.println("Lunch is being made");
    }

}

public class Dinner {

    public void makeDinner() {
        System.out.println("Dinner is being made");
    }

}

Invoker

public class MealInvoker {

    Command command;

    public MealInvoker(Command command) {
        this.command = command;
    }

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

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

}

Usage

public class Demo {

    public static void main(String[] args) {

        Lunch lunch = new Lunch(); // receiver
        Command lunchCommand = new LunchCommand(lunch); // concrete command

        Dinner dinner = new Dinner(); // receiver
        Command dinnerCommand = new DinnerCommand(dinner); // concrete command

        MealInvoker mealInvoker = new MealInvoker(lunchCommand); // invoker
        mealInvoker.invoke();

        mealInvoker.setCommand(dinnerCommand);
        mealInvoker.invoke();

    }

}

from: Command Pattern