What is an Abstract Class?

       An abstract class is one which contains some defined methods and some undefined methods. Undefined methods are alos known as unimplemented or abstract methods. Abstract classes should not be final, since they are always reusable.We cannot create an object to abstract class.

      Abstract classes are basically used to implement polymorphism.An abstract class is one which contains physical representation of abstract methods. An abstract derived class is one which contains logical declaration of abstract methods which are inherited from abstract base class.