What is the definition of polymorphism?

Polymorphism is an object-oriented programming concept that refers to the ability of a variable, function, or object to take on multiple forms. In a programming language exhibiting polymorphism, class objects belonging to the same hierarchical tree (inherited from a common parent class) may have functions with the same name, but with different behaviors.

Example:

The classic example is of the Shape class and all the classes that are inherited from it, such as:

• Rectangle

• Triangle

• Circle

Below is an example of Polymorphism:

class Shape

{

public:

Shape(){}

//defining a virtual function called Draw for shape class

virtual void Draw(){cout<<"Drawing a Shape"<<endl;}

};

class Rectangle: public Shape

{

public:

Rectangle(){}

//Draw function defined for Rectangle class

virtual void Draw(){cout<<"Drawing a Rectangle"<<endl;}

};

class Triangle: public Shape

{

public:

Triangle(){}

//Draw function defined for Triangle class

virtual void Draw(){cout<<"Drawing a Triangle"<<endl;}

};

class Circle: public Shape

{

public:

Circle(){}

//Draw function defined for Circle class

virtual void Draw(){cout<<"Drawing a Circle"<<endl;}

};

int main() {

Shape *s;

Triangle tri;

Rectangle rec;

Circle circ;

// store the address of Rectangle

s = &rec;

// call Rectangle Draw function

s->Draw();

// store the address of Triangle

s = &tri;

// call Traingle Draw function

s->Draw();

// store the address of Circle

s = &circ;

// call Circle Draw function

s->Draw();

return 0;

}

Explanation:

In the example above,

• We used virtual keyword while defining the Draw() functions as a virtual function is a member function which when declared in the base class can be re-defined (Overriden) by the derived classes.

• At run time the compiler looks at the contents of the pointer *s.

• Since, the addresses of objects of tri, rec, and circ are stored in *s the respective Draw() function is called.

As you can see, each of the child classes has a separate implementation for the function Draw(). This is how polymorphism is generally used.

Types of polymorphism:

• Compile time polymorphism

  • Example: Method overloading

• Runtime polymorphism

  • Example: Method overriding

Advantages of polymorphism:

• It helps programmers reuse code and classes once written, tested, and implemented.

• A single variable name can be used to store variables of multiple data types (float, double, long, int, etc).

• It helps compose powerful, complex abstractions from simpler ones.

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