Command pattern - Wikipedia

Contents

• 1 Uses
• 2 Terminology
• 3 Example
  • 3.1 C#
  • 3.2 Java
  • 3.3 Java 8
  • 3.4 Python
  • 3.5 Ruby
  • 3.6 Scala
  • 3.7 JavaScript
  • 3.8 Coffeescript
• 4 See also
• 5 References
• 6 External links

namespace CommandPattern
{
    using System; 
    public interface ICommand
    {
        void Execute();
    }

    /* The Invoker class */
    public class Switch
    {
        ICommand _closedCommand;
        ICommand _openedCommand;

        public Switch(ICommand closedCommand, ICommand openedCommand)
        {
            this._closedCommand = closedCommand;
            this._openedCommand = openedCommand;
        }

        //close the circuit/power on
        public void Close()
        {
           this._closedCommand.Execute();
        }

        //open the circuit/power off
        public void Open()
        {
            this._openedCommand.Execute();
        }
    }
    
    /* An interface that defines actions that the receiver can perform */
    public interface ISwitchable
    {
        void PowerOn();
        void PowerOff();
    }

    /* The Receiver class */
    public class Light : ISwitchable
    {
        public void PowerOn()
        {
            Console.WriteLine("The light is on");
        }

        public void PowerOff()
        {
            Console.WriteLine("The light is off");
        }
    }

    /* The Command for turning on the device - ConcreteCommand #1 */
    public class CloseSwitchCommand: ICommand
    {
        private ISwitchable _switchable;

        public CloseSwitchCommand(ISwitchable switchable)
        {
            _switchable = switchable;
        }

        public void Execute()
        {
            _switchable.PowerOn();
        }
    }

    /* The Command for turning off the device - ConcreteCommand #2 */
    public class OpenSwitchCommand : ICommand
    {
        private ISwitchable _switchable;

        public OpenSwitchCommand(ISwitchable switchable)
        {
            _switchable = switchable;
        }

        public void Execute()
        {
            _switchable.PowerOff();
        }
    }

    /* The test class or client */
    internal class Program
    {
        public static void Main(string[] args)
        {
            string arg = args.Length > 0 ? args[0].ToUpper() : null;

            ISwitchable lamp = new Light();

            //Pass reference to the lamp instance to each command
            ICommand switchClose = new CloseSwitchCommand(lamp);
            ICommand switchOpen = new OpenSwitchCommand(lamp);

            //Pass reference to instances of the Command objects to the switch
            Switch @switch = new Switch(switchClose, switchOpen);
            
            if (arg == "ON")
            {
                // Switch (the Invoker) will invoke Execute() (the Command) on the command object - _closedCommand.Execute();
                @switch.Close();
            }
            else if (arg == "OFF")
            {
                //Switch (the Invoker) will invoke the Execute() (the Command) on the command object - _openedCommand.Execute();
                @switch.Open();
            }
            else
            {
                Console.WriteLine("Argument \"ON\" or \"OFF\" is required.");
            }
        }
    }
}

import java.util.List;
import java.util.ArrayList;

/** The Command interface */
public interface Command {
   void execute();
}

/** The Invoker class */
public class Switch {
   private List<Command> history = new ArrayList<Command>();

   public void storeAndExecute(Command cmd) {
      this.history.add(cmd); // optional 
      cmd.execute();
   }
}

/** The Receiver class */
public class Light {

   public void turnOn() {
      System.out.println("The light is on");
   }

   public void turnOff() {
      System.out.println("The light is off");
   }
}

/** The Command for turning on the light - ConcreteCommand #1 */
public class FlipUpCommand implements Command {
   private Light theLight;

   public FlipUpCommand(Light light) {
      this.theLight = light;
   }

   @Override    // Command
   public void execute() {
      theLight.turnOn();
   }
}

/** The Command for turning off the light - ConcreteCommand #2 */
public class FlipDownCommand implements Command {
   private Light theLight;

   public FlipDownCommand(Light light) {
      this.theLight = light;
   }

   @Override    // Command
   public void execute() {
      theLight.turnOff();
   }
}

/* The test class or client */
public class PressSwitch {
   public static void main(String[] args){
      // Check number of arguments
      if (args.length != 1) {
         System.err.println("Argument \"ON\" or \"OFF\" is required.");
         System.exit(-1);
      }

      Light lamp = new Light();
      Command switchUp = new FlipUpCommand(lamp);
      Command switchDown = new FlipDownCommand(lamp);

      Switch mySwitch = new Switch();

      switch(args[0]) {
         case "ON":
            mySwitch.storeAndExecute(switchUp);
            break;
         case "OFF":
            mySwitch.storeAndExecute(switchDown);
            break;
         default:
            System.err.println("Argument \"ON\" or \"OFF\" is required.");
            System.exit(-1);
      }
   }
}

/**
 * The Command functional interface.<br/>
 */
@FunctionalInterface
public interface Command {
	public void apply();
}

/**
 * The CommandFactory class.<br/>
 */
import java.util.HashMap;
import java.util.stream.Collectors;

public final class CommandFactory {
	private final HashMap<String, Command>	commands;
	
	private CommandFactory() {
		commands = new HashMap<>();
	}

	public void addCommand(String name, Command command) {
		commands.put(name, command);
	}
	
	public void executeCommand(String name) {
		if (commands.containsKey(name)) {
			commands.get(name).apply();
		}
	}

	public void listCommands() {
		System.out.println("Enabled commands: " + commands.keySet().stream().collect(Collectors.joining(", ")));
	}
	
	/* Factory pattern */
	public static CommandFactory init() {
		CommandFactory cf = new CommandFactory();

		// commands are added here using lambdas. It is also possible to dynamically add commands without editing the code.
		cf.addCommand("Light on", () -> System.out.println("Light turned on"));
		cf.addCommand("Light off", () -> System.out.println("Light turned off"));

		return cf;
	}
}

public final class Main {
	public static void main(String[] args) {
		CommandFactory cf = CommandFactory.init();
		cf.executeCommand("Light on");
		cf.listCommands();
	}
}

class Switch(object):
    """The INVOKER class"""
    def __init__(self):
        self._history = ()

    @property
    def history(self):
        return self._history

    def execute(self, command):
        self._history = self._history + (command,)
        command.execute()

class Command(object):
    """The COMMAND interface"""
    def __init__(self, obj):
        self._obj = obj

    def execute(self):
        raise NotImplementedError

class TurnOnCommand(Command):
    """The COMMAND for turning on the light"""
    def execute(self):
        self._obj.turn_on()

class TurnOffCommand(Command):
    """The COMMAND for turning off the light"""
    def execute(self):
        self._obj.turn_off()

class Light(object):
    """The RECEIVER class"""
    def turn_on(self):
        print("The light is on")

    def turn_off(self):
        print("The light is off")

class LightSwitchClient(object):
    """The CLIENT class"""
    def __init__(self):
        self._lamp = Light()
        self._switch = Switch()

    @property
    def switch(self):
        return self._switch

    def press(self, cmd):
        cmd = cmd.strip().upper()
        if cmd == "ON":
            self._switch.execute(TurnOnCommand(self._lamp))
        elif cmd == "OFF":
            self._switch.execute(TurnOffCommand(self._lamp))
        else:
            print("Argument 'ON' or 'OFF' is required.")

# Execute if this file is run as a script and not imported as a module
if __name__ == "__main__":
    light_switch = LightSwitchClient()
    print("Switch ON test.")
    light_switch.press("ON")
    print("Switch OFF test.")
    light_switch.press("OFF")
    print("Invalid Command test.")
    light_switch.press("****")

    print("Command history:")
    print(light_switch.switch.history)

# Invoker
class Switch
  attr_reader :history

  def execute(cmd)
    @history ||= []
    @history << cmd.execute
  end
end

# Command Interface
class Command
  attr_reader :obj

  def initialize(obj)
    @obj = obj
  end

  def execute
    raise NotImplementedError
  end
end

# Command for turning on
class TurnOnCommand < Command
  def execute
    obj.turn_on
  end
end

# Command for turning off
class TurnOffCommand < Command
  def execute
    obj.turn_off
  end
end

# Receiver
class Light
  def turn_on
    'the light is on'
  end

  def turn_off
    'the light is off'
  end
end

# Client
class LightSwitchClient
  attr_reader :switch

  def initialize
    @lamp = Light.new
    @switch = Switch.new
  end

  def switch_for(cmd)
    case cmd
    when 'on'  then @switch.execute(TurnOnCommand.new(@lamp))
    when 'off' then @switch.execute(TurnOffCommand.new(@lamp))
    else puts 'Sorry, I so sorry'
    end
  end
end

client = LightSwitchClient.new
client.switch_for('on')
client.switch_for('off')
client.switch.history #=> ['the light is on', 'the light is off']

/* The Command interface */
trait Command {
   def execute()
}
 
/* The Invoker class */
class Switch {
   private var history: List[Command] = Nil
 
   def storeAndExecute(cmd: Command) {
      cmd.execute()
      this.history :+= cmd
   }
}
 
/* The Receiver class */
class Light {
   def turnOn() = println("The light is on")
   def turnOff() = println("The light is off")
}
 
/* The Command for turning on the light - ConcreteCommand #1 */
class FlipUpCommand(theLight: Light) extends Command {
   def execute() = theLight.turnOn()
}
 
/* The Command for turning off the light - ConcreteCommand #2 */
class FlipDownCommand(theLight: Light) extends Command {
   def execute() = theLight.turnOff()
}
 
/* The test class or client */
object PressSwitch {
   def main(args: Array[String]) {
      val lamp = new Light()
      val switchUp = new FlipUpCommand(lamp)
      val switchDown = new FlipDownCommand(lamp)
 
      val s = new Switch()
 
      try {
         args(0).toUpperCase match {
            case "ON" => s.storeAndExecute(switchUp)
            case "OFF" => s.storeAndExecute(switchDown)
            case _ => println("Argument \"ON\" or \"OFF\" is required.")
         }
      } catch {
         case e: Exception => println("Arguments required.")
      }
   }
}

/* The Invoker function */
"use strict";

class Switch {
  constructor() {
    this._commands = [];
  }

  storeAndExecute(command) {
    this._commands.push(command);
    command.execute();
  }
}

class Light {
  turnOn() { console.log('turn on') }
  turnOff() { console.log('turn off') }
}

class FlipDownCommand {
  constructor(light) {
    this._light = light;
  }

  execute() {
    this._light.turnOff();
  }
}

class FlipUpCommand {
  constructor(light) {
    this._light = light;
  }

  execute() {
    this._light.turnOn();
  }
}

var light = new Light();
var switchUp = new FlipUpCommand(light);
var switchDown = new FlipDownCommand(light);
var s = new Switch();

s.storeAndExecute(switchUp);
s.storeAndExecute(switchDown);

# The Invoker function
class Switch
   _commands = []
   storeAndExecute: (command) ->
     _commands.push(command)
     command.execute()

#  The Receiver function
class Light
  turnOn: ->
    console.log ('turn on')
  turnOff: ->
    console.log ('turn off')

# The Command for turning on the light - ConcreteCommand #1 
class FlipUpCommand
 constructor: (@light) ->

 execute: ->
   @light.turnOn()

# The Command for turning off the light - ConcreteCommand #2
class FlipDownCommand
 constructor: (@light) ->

 execute: ->
   @light.turnOff()

light = new Light()
switchUp = new FlipUpCommand(light)
switchDown = new FlipDownCommand(light)
s = new Switch()

s.storeAndExecute(switchUp)
s.storeAndExecute(switchDown)