Java Design Patterns Tutorial - Java Design Pattern - Command Pattern

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Command pattern is a data driven design pattern It is one of the behavioral pattern.

A request is wrapped under a object as command and passed to invoker object.

Invoker object passes the command to the corresponding object and that object executes the command.

Example

import java.util.ArrayList;
import java.util.List;
/*from  w w w.  j  ava  2s.c o  m*/
interface Command {
  void execute();
}

class MouseCursor {
  private int x = 10;
  private int y = 10;
  public void move() {
    System.out.println("Old Position:"+x +":"+y);
    x++;
    y++;
    System.out.println("New Position:"+x +":"+y);
    
  }

  public void reset() {
    System.out.println("reset");
    x = 10;
    y = 10;
  }
}

class MoveCursor implements Command {
  private MouseCursor abcStock;

  public MoveCursor(MouseCursor abcStock) {
    this.abcStock = abcStock;
  }

  public void execute() {
    abcStock.move();
  }
}

class ResetCursor implements Command {
  private MouseCursor abcStock;

  public ResetCursor(MouseCursor abcStock) {
    this.abcStock = abcStock;
  }

  public void execute() {
    abcStock.reset();
  }
}

class MouseCommands {
  private List<Command> orderList = new ArrayList<Command>();

  public void takeOrder(Command order) {
    orderList.add(order);
  }

  public void placeOrders() {
    for (Command order : orderList) {
      order.execute();
    }
    orderList.clear();
  }
}

public class Main {
  public static void main(String[] args) {
    MouseCursor cursor = new MouseCursor();

    MoveCursor moveCursor = new MoveCursor(cursor);
    ResetCursor resetCursor = new ResetCursor(cursor);

    MouseCommands commands= new MouseCommands();
    commands.takeOrder(moveCursor);
    commands.takeOrder(resetCursor);

    commands.placeOrders();
  }
}

The code above generates the following result.

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