Question

Describe a scenario/design where a polymorphic behavior is utilized. In the lecture this week we studied an example in which we defined a GeometricObject as the base class and added features to this base class to define two specialized classes, namely the Circle and the Rectangle classes. Your design should have the design elements of the example we studied but it doesn’t have to be related to geometric shapes. Clearly list the functions in the base class you would declare as virtual, what is the expected behavior? And what happens if the functions are not made virtual? Do not code, describe your design and all features of a polymorphic design requirements.

Answer 1

Consider the example given in the problem as the base is the GeometricObject and the derived classes are Circle and Rectangle.

Therefore, the structure will may be as follows:

class GeometricObject{

};

class Circle: <access_specifier> GeometricObject

{

};

class Rectangle: <access_specifier> GeometricObject

{

};

• For the polymorphism behaviour, assume that there are two functions that compute the area and the description of the class.
• The name of the area function is Area(), and of the description is Description().
• So, if we are declared these functions are virtual which is shown below, and call the functions with the pointer of the Base class, then the functions of the derived class will be called.

class GeometricObject{

public:

virtual void Area()

{

}

virtual void Description()

{

}

};

class Circle: <access_specifier> GeometricObject

{

public:

Circle(){}

void Area()

{

}

void Description()

{

}

};

class Rectangle: <access_specifier> GeometricObject

{

public:

Rectangle(){}

void Area()

{

}

void Description()

{

}

};

int main()

{

//Pointer of Base class creating the object

//of Derived classes Circle and Rectangle.

GeometricObject *object = new Circle();

GeometricObject *object1 = new Rectangle();

//Functions of the class Circle is called.

object.Area();

object.Description();

//Functions of the class Rectangle is called.

object1.Area();

object1.Description();

}

• The reason is that, the virtual keyword is used with the functions in the base class.
• The virtual keyword performs the dynamic binding and not the static binding.
• In dynamic binding, the function which is being pointed is called and not the type of pointer it is.
• Therefore, the function of Circle and Rectangle will be called.
• Now, if there is no virtual keyword with the functions.
• Then the functions of the Base class GeometricObject will be called.
• The reason is that the compiler performs the static binding.
• In static binding, the function as per the pointer in the object is being called.

Thus, for the dynamic binding or calling the functions of derived class with the pointer of the Base class, use the virtual keyword in the Base class functions.

Otherwise, compiler will always perform the static binding.