Command Pattern

Command Pattern에 대해 설명하는 페이지입니다.

Posted Oct 11, 2023

By HyunJinNo

Tags

Design Pattern, Java

1. Introduction

• Purpose
  • Encapsulates a request as an object
  • This allows the request to be handled in traditionally object based relationships such as queuing and callbacks.
• Use When
  • Requests need to be specified, queued, and executed at variant times or in variant orders.
  • A history of requests is needed.
  • The invoker should be decoupled from the object handling the invocation.

2. How to Use (Example)

• Command Interface

  java

  1public interface Command {
  2    public void execute();
  3}

• Implementing a command

  java

  1public class MyCommand implements Command {
  2    MyReceiver myRecevier;
  3
  4    public MyCommand(MyReceiver myReceiver) {
  5        this.myReceiver = myReceiver;
  6    }
  7
  8    public void execute() {
  9        // Call a method of myReceiver
  10        // ex. myReceiver.work();
  11    }
  12}

• Building Invoker

  java

  1public class MyInvoker {
  2    Command slot;
  3
  4    public MyInvoker() {}
  5
  6    public void setCommand(Command command) {
  7        slot = command;
  8    }
  9
  10    // Use your own method
  11    public void buttonPressed() {
  12        slot.execute();
  13    }
  14}

• Client Program

  java

  1public class Main {
  2    public static void main(String[] args) {
  3        // Create invoker
  4        MyInvoker myInvoker = new MyInvoker();
  5
  6        // Create receiver
  7        MyReceiver myReceiver = new MyReceiver();
  8
  9        // Create command
  10        MyCommand myCommand = new MyCommand(myReceiver);
  11
  12        // linking the invoker with the command
  13        myInvoker.setCommand(myCommand);
  14
  15        myInvoker.buttonPressed();
  16    }
  17}