Command Pattern

#designpatterns #java #pattern #behavioral

Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

Participants

Command: declares an interface for executing an operation
ConcreteCommand: defines a binding between a Receiver object and an action. Implements Execute by invoking the corresponding operation(s) on Receiver
Client: creates a ConcreteCommand object and sets its receiver
Invoker: asks the command to carry out the request
Receiver: knows how to perform the operations associated with carrying out the request.

Code

public class Main {

    public static void main(String[] args) {
        Receiver receiver = new Receiver();
        Command command = new ConcreteCommand(receiver);
        Invoker invoker = new Invoker();
        invoker.setCommand(command);
        invoker.executeCommand();
    }
}

public abstract class Command {

    protected Receiver receiver;

    public Command(Receiver receiver) {
        this.receiver = receiver;
    }

    public abstract void execute();
}

public class ConcreteCommand extends Command {

    public ConcreteCommand(Receiver receiver) {
        super(receiver);
    }

    @Override
    public void execute() {
        receiver.action();
    }
}

public class Receiver {

    public void action() {
        System.out.println("Called Receiver.action()");
    }
}

public class Invoker {

    private Command command;

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

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