Re: understanding of data abstraction, information hiding and encapsulation

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Tue, 25 Sep 2007 09:02:23 GMT
On 2007-09-25 06:42,, India wrote:

Is my following understanding correct ?

Data abstraction means providing the interface - that is, the set of
functions that can be called by the user of a class.


Information hiding means mentioning the class members(functions,
typedefs, data) under the access control labels : public, protected,

Encapsulation means providing the implementation of class member
functions and the implementation is hidden except for the inline
functions which can be present inside the class definition or the
header file which are visible to the user of a class.

The way I see it information hiding and encapsulation are more or less
the same thing, and it means that the user of the interface does not
know (or at least do not need to know) how the functionality provided by
the interface is implemented.

What this means is that when you have defined the interface and written
the code to support it a user should be able to take the code and start
using it. Later you should be able to completely replace the
implementation with a new one that provide the same interface and the
user should not have to make any changes to his/her code.

Kindly correct me if my understanding is wrong. Wherever I have gone
wrong, please provide an example C++ class so that I can understand.

A good example is the use of inheritance to define an interface and then
allow different implementations in derived classes:

#include <iostream>

class Twice
  virtual unsigned int twice(unsigned int i) = 0;

class ShiftTwice : public Twice
  unsigned int twice(unsigned int i)
    return i << 1;

class MultiplyTwice : public Twice
  unsigned int twice(unsigned int i)
    return 2 * i;

int main()
  Twice* ss = new ShiftTwice();
  Twice* ms = new MultiplyTwice();

  std::cout << ss->twice(4) << "\n";
  std::cout << ms->twice(4) << "\n";

  delete ss;
  delete ms;

Since both ShiftTwice and MultiplyTwice have the same interface they can
be used interchangeably as long as we access them through a pointer (or
reference) to Twice.

Also, does the process identification of class, its member functions
and data members, class objects, fall under data abstraction ? If not,
what is it called.

I am not sure what you are talking about, perhaps runtime type
information, but that have nothing to do with any of the above.

Erik Wikstr??m

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