命令模式

在物件導向程式設計的範疇中，命令模式（英語：Command pattern）是一種設計模式，它嘗試以物件來代表實際行動。命令物件可以把行動(action) 及其參數封裝起來，於是這些行動可以被：

• 重複多次
• 取消（如果該物件有實作的話）
• 取消後又再重做

這些都是現代大型應用程式所必須的功能，即「復原」及「重複」。除此之外，可以用命令模式來實作的功能例子還有：

• 交易行為
• 進度列
• 精靈
• 使用者介面按鈕及功能表項目
• 執行緒 pool
• 巨集收錄

結構

 

範例

C#

using System; using System.Collections.Generic; namespace CommandPattern {  public interface ICommand  {  void Execute();  }  /* The Invoker class */  public class Switch  {  private List<ICommand> _commands = new List<ICommand>();  public void StoreAndExecute(ICommand command)  {  _commands.Add(command);  command.Execute();  }  }  /* The Receiver class */  public class Light  {  public void TurnOn()  {  Console.WriteLine("The light is on");  }  public void TurnOff()  {  Console.WriteLine("The light is off");  }  }  /* The Command for turning on the light - ConcreteCommand #1 */  public class FlipUpCommand : ICommand  {  private Light _light;  public FlipUpCommand(Light light)  {  _light = light;  }  public void Execute()  {  _light.TurnOn();  }  }  /* The Command for turning off the light - ConcreteCommand #2 */  public class FlipDownCommand : ICommand  {  private Light _light;  public FlipDownCommand(Light light)  {  _light = light;  }  public void Execute()  {  _light.TurnOff();  }  }  /* The test class or client */  internal class Program  {  public static void Main(string[] args)  {  Light lamp = new Light();  ICommand switchUp = new FlipUpCommand(lamp);  ICommand switchDown = new FlipDownCommand(lamp);  Switch s = new Switch();  string arg = args.Length > 0 ? args[0].ToUpper() : null;  if (arg == "ON")  {  s.StoreAndExecute(switchUp);  }  else if (arg == "OFF")  {  s.StoreAndExecute(switchDown);  }  else  {  Console.WriteLine("Argument \"ON\" or \"OFF\" is required.");  }  }  } } 

Java

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 Switch() {  }  public void storeAndExecute(Command cmd) {  this.history.add(cmd); // optional   cmd.execute();   } } /* The Receiver class */ public class Light {  public 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;  }  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;  }  public void execute() {  theLight.turnOff();  } } /* The test class or client */ public class PressSwitch {  public static void main(String[] args){  Light lamp = new Light();  Command switchUp = new FlipUpCommand(lamp);  Command switchDown = new FlipDownCommand(lamp);  Switch mySwitch = new Switch();  try {  if ("ON".equalsIgnoreCase(args[0])) {  mySwitch.storeAndExecute(switchUp);  }  else if ("OFF".equalsIgnoreCase(args[0])) {  mySwitch.storeAndExecute(switchDown);  }  else {  System.out.println("Argument \"ON\" or \"OFF\" is required.");  }  } catch (Exception e) {  System.out.println("Arguments required.");  }  } } 

Python

class Switch(object):  """The INVOKER class"""  def __init__(self, flip_up_cmd, flip_down_cmd):  self.flip_up = flip_up_cmd  self.flip_down = flip_down_cmd  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 LightSwitch(object):  """The CLIENT class"""  def __init__(self):  lamp = Light()  self._switch = Switch(lamp.turn_on, lamp.turn_off)   def switch(self, cmd):  cmd = cmd.strip().upper()  if cmd == "ON":  self._switch.flip_up()  elif cmd == "OFF":  self._switch.flip_down()  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 = LightSwitch()  print("Switch ON test.")  light_switch.switch("ON")  print("Switch OFF test.")  light_switch.switch("OFF")  print("Invalid Command test.")  light_switch.switch("****") 

Scala

/* 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.")  }  } } 

Javascript

/* The Invoker function */ var Switch = function(){  var _commands = [];  this.storeAndExecute = function(command){  _commands.push(command);  command.execute();  } } /* The Receiver function */ var Light = function(){  this.turnOn = function(){ console.log ('turn on')};  this.turnOff = function(){ console.log ('turn off') }; } /* The Command for turning on the light - ConcreteCommand #1 */ var FlipUpCommand = function(light){  this.execute = light.turnOn; } /* The Command for turning off the light - ConcreteCommand #2 */ var FlipDownCommand = function(light){  this.execute = light.turnOff; } var light = new Light(); var switchUp = new FlipUpCommand(light); var switchDown = new FlipDownCommand(light); var s = new Switch(); s.storeAndExecute(switchUp); s.storeAndExecute(switchDown); 

C++

class ICommand {  public:  virtual void Execute() = 0; }; class Swicher {  private:  std::vector<ICommand *> _commands;  public:  void StoreAndExecute(ICommand *command)  {  if (command){  _commands.push_back(command);  command->Execute();  }  } }; class Light {  public:  void TurnOn()  {  std::cout<<"The light is on."<<std::endl;  }  void TurnOff()  {  std::cout << "The light is off." << std::endl;  } }; /* The Command for turning on the light - ConcreteCommand #1 */ class FlipUpCommand : public ICommand {  private:  Light *_light;  public:  FlipUpCommand(Light *light)  {  _light = light;  }  void Execute()  {  _light->TurnOn();  } }; /* The Command for turning off the light - ConcreteCommand #2 */ class FlipDownCommand : public ICommand {  private:  Light *_light;  public:  FlipDownCommand(Light *light)  {  _light = light;  }  void Execute()  {  _light->TurnOff();  } }; int main() {  Light *light = new Light();  ICommand *switchOn = dynamic_cast<ICommand *>(new FlipUpCommand(light));  ICommand *switchDown = dynamic_cast<ICommand *>(new FlipDownCommand(light));  Swicher *switcher = new Swicher();  switcher->StoreAndExecute(switchOn);  switcher->StoreAndExecute(switchDown);  delete switcher;  delete switchOn;  delete switchDown;  delete light; }