Decorator Pattern | Set 3 (Coding the Design)

We have discussed Pizza design problem and different naive approaches to solve it in set 1. We have also introduced Decorator pattern in Set 2. In this article, design and implementation of decorator pattern for Pizza problem is discussed. It is highly recommended that you try it yourself first. The new class diagram (Click on the picture to see it clearly)

• Pizza acts as our abstract component class.
• There are four concrete components namely PeppyPaneer , FarmHouse, Margherita, ChickenFiesta.
• ToppingsDecoratoris our abstract decorator and FreshTomato , Paneer, Jalapeno, Barbeque are concrete decorators.

Below is the java implementation of above design. 

Java

// Java program to demonstrate Decorator
// pattern

// Abstract Pizza class (All classes extend
// from this)
abstract class Pizza
{
    // it is an abstract pizza
    String description = "Unkknown Pizza";

    public String getDescription()
    {
        return description;
    }

    public abstract int getCost();
}

// The decorator class :  It extends Pizza to be
// interchangeable with it toppings decorator can
// also be implemented as an interface
abstract class ToppingsDecorator extends Pizza
{
    public abstract String getDescription();
}

// Concrete pizza classes
class PeppyPaneer extends Pizza
{
    public PeppyPaneer() { description = "PeppyPaneer"; }
    public int getCost() {  return 100; }
}
class FarmHouse extends Pizza
{
    public FarmHouse() {  description = "FarmHouse"; }
    public int getCost() { return 200; }
}
class Margherita extends Pizza
{
    public Margherita()  { description = "Margherita"; }
    public int getCost() { return 100;  }
}
class ChickenFiesta extends Pizza
{
    public ChickenFiesta() { description = "ChickenFiesta";}
    public int getCost() { return 200; }
}
class SimplePizza extends Pizza
{
public SimplePizza() { description = "SimplePizza"; }
public int getCost() {  return 50;  }
}

// Concrete toppings classes
class FreshTomato extends ToppingsDecorator
{
    // we need a reference to obj we are decorating
    Pizza pizza;

    public FreshTomato(Pizza pizza) { this.pizza = pizza; }
    public String getDescription() {
        return pizza.getDescription() + ", Fresh Tomato ";
    }
    public int getCost() { return 40 + pizza.getCost(); }
}
class Barbeque extends ToppingsDecorator
{
    Pizza pizza;
    public Barbeque(Pizza pizza) {  this.pizza = pizza;  }
    public String getDescription() {
        return pizza.getDescription() + ", Barbeque ";
    }
    public int getCost() { return 90 + pizza.getCost(); }
}
class Paneer extends ToppingsDecorator
{
    Pizza pizza;
    public Paneer(Pizza pizza)  {  this.pizza = pizza; }
    public String getDescription() {
        return pizza.getDescription() + ", Paneer ";
    }
    public int getCost()  {  return 70 + pizza.getCost(); }
}

// Other toppings can be coded in a similar way

// Driver class and method
class PizzaStore
{
    public static void main(String args[])
    {
        // create new margherita pizza
        Pizza pizza = new Margherita();
        System.out.println( pizza.getDescription() +
                         " Cost :" + pizza.getCost());

        // create new FarmHouse pizza
        Pizza pizza2 = new FarmHouse();

        // decorate it with freshtomato topping
        pizza2 = new FreshTomato(pizza2);

        //decorate it with paneer topping
        pizza2 = new Paneer(pizza2);

        System.out.println( pizza2.getDescription() +
                         " Cost :" + pizza2.getCost());
        Pizza pizza3 = new Barbeque(null);    //no specific pizza
        System.out.println( pizza3.getDescription() + "  Cost :" + pizza3.getCost());
   }
}

Output:

Margherita Cost :100
FarmHouse, Fresh Tomato , Paneer Cost :310

Notice how we can add/remove new pizzas and toppings with no alteration in previously tested code and toppings and pizzas are decoupled. 

CPP

// CPP program to demonstrate
// Decorator pattern
#include <iostream>
#include <string>
using namespace std;

// Component
class MilkShake
{
public:
    virtual string Serve() = 0;
    virtual float price() = 0;
};


// Concrete Component
class BaseMilkShake : public MilkShake
{
public:
    string Serve()
    {
        return "MilkShake";
    }

    float price()
    {
        return 30;
    }
};

// Decorator
class MilkShakeDecorator: public MilkShake
{
protected:
    MilkShake *m_MilkShake;
public:

    MilkShakeDecorator(MilkShake *baseMilkShake): m_MilkShake(baseMilkShake){}

    string Serve()
    {
        return m_MilkShake->Serve();
    }

    float price()
    {
        return m_MilkShake->price();
    }
};


// Concrete Decorator
class MangoMilkShake: public MilkShakeDecorator
{
public:
    MangoMilkShake(MilkShake *baseMilkShake): MilkShakeDecorator(baseMilkShake){}

    string Serve()
    {
        return m_MilkShake->Serve() + " decorated with Mango ";
    }
    float price()
    {
        return m_MilkShake->price() + 40;
    }
};


class VanillaMilkShake: public MilkShakeDecorator
{
public:
    VanillaMilkShake(MilkShake *baseMilkShake): MilkShakeDecorator(baseMilkShake){}

    string Serve()
    {
        return m_MilkShake->Serve() + " decorated with Vanilla ";
    }
    float price()
    {
        return m_MilkShake->price() + 80;
    }
};

int main()
{
  MilkShake *baseMilkShake = new BaseMilkShake();
  cout << "Basic Milk shake \n";
  cout << baseMilkShake -> Serve() << endl;
  cout << baseMilkShake -> price() << endl;

  MilkShake *decoratedMilkShake = new MangoMilkShake(baseMilkShake);
  cout << "Mango decorated Milk shake \n";
  cout << decoratedMilkShake -> Serve() << endl;
  cout << decoratedMilkShake -> price() << endl;

  delete decoratedMilkShake;

  decoratedMilkShake = new VanillaMilkShake(baseMilkShake);
  cout << "Vanilla decorated Milk shake \n";
  cout << decoratedMilkShake -> Serve() << endl;
  cout << decoratedMilkShake -> price() << endl;

 delete decoratedMilkShake;
 delete baseMilkShake;
  return 0;
}

Output:

Basic Milk shake
MilkShake
Price of MilkShake : 30
Mango decorated Milk shake
MilkShake decorated with Mango
Price of Mango MilkShake : 70
Vanilla decorated Milk shake
MilkShake decorated with Vanilla
Price of Vanilla MilkShake : 110

Further Read: Decorator Method in Python

This article is contributed by Sulabh Kumar and Shashank Gupta. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above