Design Patterns - Command Pattern

https://dzone.com/articles/design-patterns-command
http://javapapers.com/design-patterns/command-design-pattern/

The following information is copied from the above links..






Command declares an interface for all commands, providing a simple execute() method which asks the Receiver of the command to carry out an operation.

java.lang.Runnable
javax.swing.Action

Command is an interface with execute method. It is the core of contract.

//Command

public interface Command{

  public void execute();

}

A Command implementation’s instance creates a binding between the receiver and an action

//Concrete Command






public class LightOnCommand implements Command{
  //reference to the light


   Light light;






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






  public void execute(){
     light.switchOn();
}






}







//Concrete Command






public class LightOffCommand implements Command{






  //reference to the light
  Light light;


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






  public void execute(){
    light.switchOff();
  }






}





Receiver is the object that knows the actual steps to perform the action.


Receiver Class


//Receiver

public class Light{







  private boolean on;







  public void switchOn(){
    on = true;
  }







  public void switchOff(){







    on = false;







  }







}



An invoker instructs the command to perform an action.




//Invoker
public class RemoteControl{
  private Command command;
  public void setCommand(Command command){
    this.command = command;
  }
  public void pressButton(){
    command.execute();
  }
}

A client creates an instance of a command implementation and associates it with a receiver.



//Client






public class Client{






  public static void main(String[] args)    {






    RemoteControl control = new RemoteControl();






    Light light = new Light();






    Command lightsOn = new LightsOnCommand(light);






    Command lightsOff = new LightsOffCommand(light);













    //switch on






    control.setCommand(lightsOn);






    control.pressButton();













    //switch off






    control.setCommand(lightsOff);






    control.pressButton();






  }






}