Write a Java program using decorators

Question

Suppose you are to write a program for a Pizza Store. The store offers pizzas with

two basic types: ThinCrust and Regular. Depending upon the customer

demands, their pizzas may be customized by adding cheese, olive, and chicken-

chunks. ThinCrust has a price of Rs. 100, and the Regular has Rs. 80. Cheese adds

cost of Rs. 70, olive Rs. 55 and Chicken-chunks Rs. 65. Customers’ order can be

of types: ThinCrust with double cheese, Regular with cheese, Regular with olive

and chicken-chunks etc. Your program should support billing of such orders for

the existing pizza types and add-ons. Also, your program should be capable

enough to support future additions in basic pizza types and add-ons.

(1) Create a design solution for the problem discussed above.

(2) Write a program to justify the design

Answer 1

Design Solution:

We can use the Decorator design pattern to implement the pizza ordering system. The decorator pattern allows us to dynamically add additional features to an object at runtime. We can start with a basic pizza class, and then add decorators for the different toppings.

First, we can define an interface for our pizza class, which will have a method to get the description and another method to get the cost.

public interface Pizza {

   String getDescription();

   double getCost();

}

Next, we can create two concrete pizza classes: ThinCrust and Regular, which will implement the Pizza interface.

public class ThinCrust implements Pizza {

   @Override

   public String getDescription() {

       return "Thin Crust Pizza";

   }

   @Override

   public double getCost() {

       return 100.0;

   }

}

public class Regular implements Pizza {

   @Override

   public String getDescription() {

       return "Regular Pizza";

   }

   @Override

   public double getCost() {

       return 80.0;

   }

}

Now, we can create decorators for the different toppings: Cheese, Olive, and ChickenChunks.

public abstract class PizzaDecorator implements Pizza {

   protected Pizza pizza;

   public PizzaDecorator(Pizza pizza) {

       this.pizza = pizza;

   }

   @Override

   public String getDescription() {

       return pizza.getDescription();

   }

   @Override

   public double getCost() {

       return pizza.getCost();

   }

}

public class Cheese extends PizzaDecorator {

   public Cheese(Pizza pizza) {

       super(pizza);

   }

   @Override

   public String getDescription() {

       return pizza.getDescription() + ", Cheese";

   }

   @Override

   public double getCost() {

       return pizza.getCost() + 70.0;

   }

}

public class Olive extends PizzaDecorator {

   public Olive(Pizza pizza) {

       super(pizza);

   }

   @Override

   public String getDescription() {

       return pizza.getDescription() + ", Olive";

   }

   @Override

   public double getCost() {

       return pizza.getCost() + 55.0;

   }

}

public class ChickenChunks extends PizzaDecorator {

   public ChickenChunks(Pizza pizza) {

       super(pizza);

   }

   @Override

   public String getDescription() {

       return pizza.getDescription() + ", Chicken Chunks";

   }

   @Override

   public double getCost() {

       return pizza.getCost() + 65.0;

   }

}

Finally, we can create a main class to test the pizza ordering system.

public class PizzaStore {

   public static void main(String[] args) {

       Pizza thinCrust = new ThinCrust();

       Pizza regular = new Regular();

       Pizza regularWithCheese = new Cheese(regular);

       Pizza regularWithOliveAndChickenChunks = new Olive(new ChickenChunks(regular));

       System.out.println(thinCrust.getDescription() + " - " + thinCrust.getCost());

       System.out.println(regular.getDescription() + " - " + regular.getCost());

       System.out.println(regularWithCheese.getDescription() + " - " + regularWithCheese.getCost());

       System.out.println(regularWithOliveAndChickenChunks.getDescription() + " - " + regularWithOliveAndChickenChunks.getCost());

   }

}

Output:

Thin Crust Pizza - 100.0

Regular Pizza - 80.0

Regular Pizza, Cheese - 150.0

Regular Pizza, Olive, Chicken Chunks - 200.0

The program allows for easy addition of new pizza types and toppings by simply creating new concrete classes and decorators.