Aae oop xp_03

Encapsulation and Abstraction

Objectives
In this lesson, you will learn to:
Define Abstraction
Define Encapsulation
State the relationship between abstraction and
encapsulation
Implement encapsulation in C++ using the private and
public access specifiers
Use static variables and functions
Use friend functions and classes

©NIIT OOPS/Lesson 3/Slide 1 of 21


Abstraction
Denotes the essential characteristics of an object that
distinguishes it from all other kinds of objects
Provides defined conceptual boundaries relative to the
perspective of the viewer



Encapsulation
Is a process of hiding all the details of an object that
do not contribute to its essential characteristics
Prevents access to non-essential details
Is also called information hiding or data hiding



Relationship Between Abstraction and
Encapsulation
Complement each other
Encapsulation assists abstraction by providing a
means of suppressing the non-essential details



Implementing Abstraction and Encapsulation
using Access Specifiers
Public access specifier
Allows a class to expose its member variables and
member functions to other functions and objects
Example:
#includeiostream
class Car
{
public:
char color[21];
};



using Access Specifiers (Contd.)
int main()
{
Car ford;
/* The . operator is used
to access member data and
functions */
cin ford.color; /*Since
the color variable is public, it can
be accessed outside the class
definition.*/
return 0;
}



Private access specifier
Allows a class to hide its member variables and
member functions from other class objects and
functions
Offers data hiding by protecting data from external
alteration



Protected access specifier
Allows a class to hide its member variables and
member functions from other class objects and
functions just like private access specifier - is
used while implementing inheritance




Visible to
Visible to own objects of
Access specifier
class members same/other
class

public Yes Yes

private Yes No

protected Yes No



Just a Minute...
You have defined a Customer class as part of
developing the billing system software for Diaz
Telecommunications Inc. The class, which you’ve
defined, is as follows:
class Customer
{
private:
char mobileNo[11];
char name[25];
char dateOfBirth[11];
void print()
{
//code to print the customer details
}


Just a Minute...(Contd.)
public:
char billingAddress[51];
char city[25];
char phoneNo[11];
float amountOutstanding;
void get()
{
//code to accept the customer details
}
};
The Customer class definition shown above is
incorrect. Identify the errors in the Customer class and
write the correct definition for it.


Static Variables
Retain their values even after the function to which
they belong has been executed
Example:
class staticExample
{
int data;
static int staticVar; // static
//variable declared
public:
//Definition of member function
};



Static Functions
Can only access static variables
Are accessed using class names



Problem Statement 3.P.1
You have defined a Dealer class as part of developing
the billing system software for Diaz Telecommunications
Inc. The class, which you’ve defined, is as follows:

class Dealer
{
private:
char mobileNo[11];
char dealerName[25];
char dealerAddress[51];
char dealerCity[25];
char phoneNo[11];



Problem Statement 3.P.1 (Contd.)
public:
static int CompanyID
void showID()
{
coutThe dealer name
isdealerName;
coutThe company ID isCompanyID;
}
void get()
{
//code to accept the dealer details
}


Problem Statement 3.P.1 (Contd.)
void print()
{
//code to print the dealer details
}
};
int CompanyID=6519;

The Dealer class definition shown above is incorrect.
Identify the errors in the Dealer class and write a
correct definition for it.



Friend Functions and Classes
Friend functions
Can be any non-member functions declared by a
class
May directly access the private member attributes
and methods of the class objects
Friend classes
Can also be made a friend of another class



Summary
In this lesson, you learned that:
Abstraction denotes the essential characteristics of an
object that distinguishes it from all other kinds of
objects and thus provides crisply defined conceptual
boundaries, relative to the perspective of the viewer
Encapsulation is the process of hiding all of the details
of an object that do not contribute to its essential
characteristics
An access specifier is used to determine whether any
other class or function can access the member
variables and functions of a particular class



Summary (Contd.)
C++ supports three access specifiers:
public
private
protected
The public access specifier allows a class to subject
its member variables and member functions to other
functions and objects
The private access specifier allows a class to hide
its member variables and member functions from other
class objects and functions



Summary (Contd.)
The protected access specifier allows a class to
hide its member variables and member functions from
other class objects and functions just like private
access specifier - is used while implementing
inheritance
The static variable retains its value even after the
function to which it belongs has been executed
Static functions can only access static variables; non-
static variables cannot be accessed using static
functions



Summary (Contd.)
Any non-member function may be declared a friend
by a class, in which case the function may directly
access the private member attributes and methods
of the class objects
A class can also be made a friend of another class


Aae oop xp_03

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