Question

I am confused about abstraction and encapsulation.What i feel is that class is encapsulation as it encapsulates data and behaviour,while interface is abstraction.Please comment

Answer 1

I think your terminology is confused.

1. Encapsulation – puts related data and functionality in one place. We can get this through classes

2. Polymorphism – Allows values of different data types to be handled using a uniform interface.

Polymorphism can be achieved by inheriting base classes (with virtual functions) and/or by implementing interfaces.

These techniques (and others) give us abstraction, which really applies to any of the processes we use to break a problem up into smaller components.

EDIT

Q) You ask “Can i say,abstraction is the topmost hierarchy which is accomplished through encapsulation and polymorphism?”

A) I can’t answer that question, I don’t know what you mean by “topmost” and “highest”.
There is no hierarchy here.

Functional Decomposition is a form of abstraction, it can be achieved without using Object Orientation, where should it come in the hierarchy?

The best I can do with a hierarchy is this definition (straight out of my own head, so YMMV)

1. Abstraction is the practice of
   breaking a large problem into
   smaller components, so each smaller
   problem can be worked on in
   (relative) isolation.
2. Polymorphism is a technique we can
   use to achieve abstraction. It
   involves identifying different types
   of data and behavior that can be
   treated in an homogeneous manner.
3. An interface only declares types of
   behaviour, encapsulating the
   behaviour in a type. It provides no
   actual behaviour or data
4. An abstract class declares types of
   behaviour, but may also provide
   behaviour and data, all encapsulated
   in a type.
5. Therefore, an interface can be seen
   as providing a simpler or purer
   form of polymorphism than abstract
   classes.