What is polymorphism?

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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