Command

The intent of the command pattern is to turn commands into stand-alone objects so that the object invoking the command does not need to worry about how the command is done. By doing so you can delay, queue, undo commands.

Structure

Example


// Client
public class CommandPatternDemo {
   public static void main(String[] args) {
      Stock abcStock = new Stock();
 
      BuyStock buyStockOrder = new BuyStock(abcStock);
      SellStock sellStockOrder = new SellStock(abcStock);
 
      Broker broker = new Broker();
      broker.takeOrder(buyStockOrder);
      broker.takeOrder(sellStockOrder);
 
      broker.placeOrders();
   }
}
// Command Interface
public interface Order {
 void execute(); 
}
// Receiver
public class Stock {
   private String name = "ABC";
   private int quantity = 10;
 
   public void buy(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] bought");
   }
   public void sell(){
      System.out.println("Stock [ Name: "+name+", 
         Quantity: " + quantity +" ] sold");
   }
}
// ConcreteCommands
public class BuyStock implements Order {
   private Stock abcStock;
 
   public BuyStock(Stock abcStock){
      this.abcStock = abcStock;
   }
 
   public void execute() {
      abcStock.buy();
   }
}
public class SellStock implements Order {
   private Stock abcStock;
 
   public SellStock(Stock abcStock){
      this.abcStock = abcStock;
   }
 
   public void execute() {
      abcStock.sell();
   }
}  
// Invoker
public class Broker {
   private List<Order> orderList = new ArrayList<Order>(); 
 
   public void takeOrder(Order order){
      orderList.add(order);  
   }
 
   public void placeOrders(){
      for (Order order : orderList) {
         order.execute();
      }
      orderList.clear();
   }
}