Polymorphism

Polymorphism is the ability of an object to take on many forms. In OOP polymorphism is implemented by the Inheritance.

In Java, any class is polymorphic. Any class Is-A Object, meanwhile IS-A form of itself. At least, a class has two forms.

An abstract class, a superclass, or an interface, may have different forms due to their derivatives.  A derivative may have many different forms.

Virtual method refers to a method is a method that is overridden by a child class. Its implementation is determined by its run time implementation instance.