Here, car is the end product. So class Car created as interface which has two pure virtual functions. The class implements it has to provide the definitions of these functions.
//Interface class
class ICar
{
public:
virtual void printCarModel() = 0;
virtual uint32_t getCost() = 0;
};
2. Concrete component class:
As car company is selling the three different car models, created concrete component class for each car type which is inherited from the Car interface class . These concrete classes has the cost of the respective car model.
/************* CONCRETE COMPONENT CLASS ********************/
//Sedan
class CSedan : public ICar
{
private:
uint32_t cost;
public:
//constructor
CSedan()
{
//cost of this car model
cost = 1000000;
}
//Implementation of the pure virtual methods declared in the Interface class
void printCarModel() override
{
cout<<" : car model is Sedan "<<endl;
}
uint32_t getCost() override
{
cout << "car cost "<<cost << " "<<endl;
return cost;
}
};
//mini
class CMini : public ICar
{
private:
uint32_t cost;
public:
//constructor
CMini()
{
//cost of this car model
cost = 650000;
}
//Implementation of the pure virtual methods declared in the Interface class
void printCarModel() override
{
cout<<" : car model is Mini "<<endl;
}
uint32_t getCost() override
{
cout << "car cost "<<cost << " "<<endl;
return cost;
}
};
//XUV
class CXUV : public ICar
{
private:
uint32_t cost;
public:
//constructor
CXUV()
{
//cost of this car model
cost = 1500000;
}
//Implementation of the pure virtual methods declared in the Interface class
void printCarModel() override
{
cout<<" : car model is XUV "<<endl;
}
uint32_t getCost() override
{
cout << "car cost "<<cost << " "<<endl;
return cost;
}
};
3.Base decorator abstract class:
Since car company is offering additional features to choose, created base decorator abstract class which is derived from ICar interface class.
This class contains the object of the interface class, and the implementations of the pure virtual functions defined in the interface class. Interface class object is assigned in the constructor call.
Additionally this class provides either pure virtual function or abstract function for the additional features or both.
//Decorator class
class CCarDecorator:public ICar
{
private:
//interface class object
ICar* car;
public:
//constructor
CCarDecorator(ICar* carObject)
{
car = carObject;
}
//Implementation of the pure virtual methods declared in the Interface class
void printCarModel() override
{
car->printCarModel();
}
uint32_t getCost() override
{
return car->getCost();
}
//additional features
virtual void additionalFeatures() = 0;
};
4.Concrete decorator class:
As car company is offering three additional features, added three concrete decorator classes which are derived from base decorator class.
In the constructor call, this class calls the constructor of the base decorator class and pass the instance of the ICar class.
These classes either provides the implementation of the pure virtual methods declared in the interface class or uses the implementation available from the base decorator class. Also these classes contains the functions for additional features to add on top of the concrete component class.
//AirBag feature
class CAirBags:public CCarDecorator
{
public:
//Enum for air bag types
enum eAirBagType
{
eFront = 0,
eBack
};
//constructor
CAirBags(ICar* carObject,eAirBagType type):CCarDecorator(carObject)
{
//car object and type of the air bag selected by the customer passed as argument
//of the constrcutor call
airBagSupport = type;
//cost calculations
if(eFront == airBagSupport)
{
costOfAirBags = 20000;
}
else if(eBack == airBagSupport)
{
costOfAirBags = 40000;
}
else{
airBagSupport = eFront;
costOfAirBags = 20000;
}
}
//additional features
uint32_t getCost() override
{
cout <<"Airbag cost = "<< costOfAirBags <<" ";
return CCarDecorator::getCost() + costOfAirBags;
}
void printCarModel() override
{
additionalFeatures();
CCarDecorator::printCarModel();
}
void additionalFeatures() override
{
cout<<"airbags added for "<<((eFront == airBagSupport) ? " front passengers " : "front and back passengers ");
}
private:
//air bag cost
uint32_t costOfAirBags;
//type of the air bag selected by the user
eAirBagType airBagSupport;
};
//Rear Camera
class CRearCamera:public CCarDecorator
{
private:
uint32_t costOfRearCamera;
public:
//car object and type of the air bag selected by the customer passed as argument
//of the constrcutor call
CRearCamera(ICar* carObject):CCarDecorator(carObject)
{
costOfRearCamera = 250000;
}
//Additional features
uint32_t getCost() override
{
cout <<"cost of rearcamera = "<< costOfRearCamera <<" ";
return CCarDecorator::getCost() + costOfRearCamera;
}
void additionalFeatures() override
{
cout<<"rear camera added ";
}
void printCarModel() override
{
additionalFeatures();
CCarDecorator::printCarModel();
}
};
class CEntertainmentUnit:public CCarDecorator
{
public:
//enum for HU models
enum eHUModel
{
eBasic = 0,
eMedium = 1,
eAdvanced
};
//car object and type of the air bag selected by the customer passed as argument
//of the constrcutor call
CEntertainmentUnit(ICar* carObject,eHUModel type):CCarDecorator(carObject)
{
HUModel = type;
if(eBasic == HUModel)
{
costOfHU = 20000;
}
else if(eMedium == HUModel)
{
costOfHU = 32000;
}
else if(eAdvanced == HUModel)
{
costOfHU = 45000;
}
}
//Additional features
uint32_t getCost() override
{
cout << "HU cost " << costOfHU <<" ";
return CCarDecorator::getCost() + costOfHU;
}
void additionalFeatures() override
{
cout<<"Entertainment unit added with Model "<<((HUModel == eBasic )?" Basic ":((HUModel == eMedium ) ? "Medium " : "Advanced "))<<" , ";
}
void printCarModel() override
{
additionalFeatures();
CCarDecorator::printCarModel();
}
private:
uint32_t costOfHU; //cost of the HU
eHUModel HUModel; //HU model types
};
Client code:
void testDecoratorpattern()
{
//Chosing sedan with front and back airbags and Medium type HU model
ICar* carModel = new CSedan;
carModel = new CAirBags(carModel, CAirBags::eBack);
carModel = new CEntertainmentUnit(carModel, CEntertainmentUnit::eMedium);
carModel->printCarModel();
cout <<endl << "cost = "<<carModel->getCost();
//Chosing Mini with front airbags and basic type HU model
carModel = new CMini;
carModel = new CAirBags(carModel, CAirBags::eFront);
carModel = new CEntertainmentUnit(carModel, CEntertainmentUnit::eBasic);
carModel->printCarModel();
cout <<endl << "cost = "<<carModel->getCost();
//Chosing XUV with rear camera, front and back airbags and advanced type HU model
carModel = new CXUV;
carModel = new CRearCamera(carModel);
carModel = new CEntertainmentUnit(carModel, CEntertainmentUnit::eAdvanced);
carModel = new CAirBags(carModel, CAirBags::eBack);
carModel->printCarModel();
cout <<endl <<"cost = "<<carModel->getCost();
}
Program output:
