Decorator Design Pattern

Decorator Design Pattern: -

                                      “Adding some extra class ,function or object to an original class without changing its structure is called decorator pattern.”

It helps user to add some extra functionality in existing class, this type of design pattern comes under structural pattern because it behaves like a wrapper to existing class.

Decorator pattern is nothing but just decorating a class adding some extra element in that class.

Consider a demo example shown below.in this the original class is house consisting of walls, step, roof. Now we are decorating this house by adding window doors, doors by using their respective classes.

Code:-

#include<iostream>

using namespace std;

class House

{

public:

   virtual void draw() = 0;

    virtual ~House()

    {

    }

};

class NormalHouse:public House

{

public:

    void draw()

    {

        cout<<"Walls + Step + roof";

    }

};

class HouseDecorator:public House

{

public:

    HouseDecorator(House& dd):D_Decorator(dd)

    {

    }

    void draw()

    {

        D_Decorator.draw();

    }

private:

    House& D_Decorator;

};

class Door:public HouseDecorator

{

public:

    Door(House& dd):HouseDecorator(dd)

    {

    }

    void draw()

    {

        HouseDecorator::draw();

        cout<<"+Door";

    }

};

class Windowdoor:public HouseDecorator

{

public:

    Windowdoor(House& dd):HouseDecorator(dd)

    {

    }

    void draw()

    {

        //HouseDecorator::draw();

        cout<<"+Windowdoor"<<endl;

    }

};

int main()

{

    House* h=new NormalHouse();

    h->draw();

    House* d= new Door(*h);

    d->draw();

    House* w=new Windowdoor(*d);

    w->draw();

    return 0;

}

Result:-

references:

https://cppcodetips.wordpress.com/2016/10/31/decorator-pattern-explained-with-c-sample/

         

Example of Abstact Factory Design Pattern

As we discussed in last block  'what is meant by abstract factory design pattern?'. In this block I am going to discussed about CPP example of Abstract Factory Design Pattern.

The main difference between factory design and abstract factory design is that in factory design pattern construct single object and abstract factory construct multiple object.Procedure for writing CPP code for Abstract Factory Design Pattern is as follow:

• Create the abstract product
• Create the concrete product
• Create abstract factor
• Create concrete factories (with related/ dependent object)
• Create client

Code for Book example which we discussed in last block

              #include <iostream>

              #define BIOGRAPHY

              //define NOVEL

              using namespace std;

             class Book     //Create Abstract Product

            { public:

                     virtual void draw() = 0;

             };

             class BiographyPrice : public Book     //Create Concrete product 1

            { public:

                     void draw() { cout << "Price:500\n"; }

             };

            class BiographyAuthor : public Book                 

            { public:

                     void draw() { cout << "Author: Arun Tiwari\n"; }

            };

            class NovelPrice : public Book                         //Create Concrete product 2

           {public:

                      void draw() { cout << "Price:600\n"; }

            };

            class NovelAuthor : public Book

           { public:

                       void draw() { cout << "Author: Henry Fielding\n"; }

            };

            class Factory                    //Create Abstract Factory

           { public:

                       virtual Book *Price() = 0;

                       virtual Book *Author() = 0;

            };

           class BiographyFactory : public Factory               //Concrete factory 1

           { public:

                       Book *Price() { return new BiographyPrice; }

                       Book *Author() {  return new BiographyAuthor; }

           };

           class NovelFactory : public Factory                        //Concrete factory 2

           { public:

                       Book *Price() { return new NovelPrice; }

                       Book *Author() { return new NovelAuthor;  }

           };

           class Client                                  //Create client

           { private:

                        Factory *factory;

             public:

                       Client(Factory *f)

                      { factory = f; }

                       void draw()

                     { Book *b = factory->Price();

                        b->draw();

                       display_window_one();

                       display_window_two();

          }

          void display_window_one()

         { Book *b[] = {

                      factory->Price(),

                      factory->Author()

                     };

                     b[0]->draw();

                     b[1]->draw();

          }

           void display_window_two()

          { Book *b[] =

                    {  factory->Price(),

                        factory->Author()

                     };

                     b[0]->draw();

                     b[1]->draw();

          } };

int main()

        { Factory *factory;

           #ifdef BIOGRAPHY

           factory = new BiographyFactory;

           #else // NOVEL

           factory = new NovelFactory;

           #endif

          Client *c = new Client(factory);

           c->draw();

         }

RESULT:

Link of  Blog: https://drive.google.com/a/vit.edu/file/d/1MvcuWT7pAIlq19Hs102N4MwEGwnP1-3y/view?usp=drivesdk