03 iec t1_s1_oo_ps_session_04

Object-Oriented Programming Using C#
Objectives

In this session, you will learn to:
Define abstraction and encapsulation
Implement encapsulation by using access specifiers
Use methods

Ver. 1.0 Session 4 Slide 1 of 26

Introducing Abstraction and Encapsulation

Abstraction and encapsulation are important features of any
object-oriented programming language.
Abstraction involves extracting only the relevant information.
Encapsulation involves packaging one or more components
together.


Defining Abstraction

An automobile salesperson is aware that different people
have different preferences.
Some people are interested in the speed of a car, some in its
price, some in the engine, and the some in its style.
Although all of them want to buy a car, each of them is
interested in a specific attribute or feature.
The salesman knows all the details of a car, but he presents
only the relevant information to a potential customer.
As a result, a the salesman practices abstraction and presents
only relevant details to customer.


Defining Encapsulation

Encapsulation literally means ‘to enclose in or as if in a
capsule’.
Encapsulation is defined as the process of enclosing one or
more items within a physical or logical package.
It involves preventing access to nonessential details.


Implementing Encapsulation by Using Access Specifiers

An access specifier defines the scope of a class member.
A class member refers to the variables and functions in a
class.
A program can have one or more classes.
You may want some members of a class to be accessible to
other classes.
But, you may not want some other members of the class to
be accessible outside the class.


Types of Access Specifiers

C# supports the following access specifiers:
public
private
protected
internal
protected internal


Demo: Calculating Area and Volume by Using Access Specifiers

Problem Statement:
Write a program to calculate the area of a rectangle and a
square.


Using Methods

A method is a set of one or more program statements,
which can be executed by referring to the method name.
To use methods, you need to:
Define methods
Call methods


Defining Methods

Defining a method means declaring the elements of its
structure.
Consider the syntax of defining a method:
<Access specifier> <Return Type> <Method
Name>(Parameter List)
{
Method Body
}


Defining Methods (Contd.)

The elements of the method declaration include the method
name, the parameters list, the return type, and the method
body.
The following are the elements of a method:
Access specifier
Return type
Method name
Parameter list
Method body
Let us understand each of the element of the method
declaration.



Defining a method means declaring the
This determines the
elements of its structure. extent to which a
Consider the syntax of defining avariable or method
method: can be accessed
<Access specifier> <Return Type> from another class.
<Method Name>(Parameter List)
{
Method Body
}



A method can return
Defining a method means declaring the
elements of its structure. a value of any type.
Consider the syntax of defining aIf the method is not
method: returning any value,
<Access specifier> <Return Type> use void as the
<Method Name>(Parameter List) return type.
{
Method Body
}



Defining a method means declaring the This is a unique
elements of its structure. identifier and is
Consider the syntax of defining a method: case-sensitive.
<Access specifier> <Return Type> The method name
<Method Name>(Parameter List) cannot be the
{ same as the
Method Body
variable name or
any other
}
non-method item
declared in the
class.



Defining a method means declaring the This is used to
elements of its structure. pass and receive
Consider the syntax of defining a method: the data from a
<Access specifier> <Return Type> method. It is
<Method Name>(Parameter List) enclosed between
{ parentheses. The
Method Body
parentheses are
included even if
}
there are no
parameters.



Defining a method means declaring the This contains the
elements of its structure. set of instructions
Consider the syntax of defining a needed to complete
method: the required activity.
<Access specifier> <Return Type>
<Method Name>(Parameter List)
{
Method Body
}


Calling Methods

After defining the method, you can execute it by calling it.
You can call a method by using the name of the method.
The method name is followed by parentheses even if the
method call has no parameters, as shown in the following
example:
MethodName();


Calling Methods (Contd.)

The following is an example of calling methods:
using System;
class Calculator
{
public int AddNumber(int num1, int num2)
{
int result;
result = num1 + num2;
return result;
}
static void Main(string[] args)


Calling Methods (Contd.)

{
Calculator cal = new Calculator();
// The following statement is calling the
// AddNumber method and passing 10 and
// 20 as the parameter list.
int value=cal.AddNumber(10, 20);
Console.WriteLine("The result is
{0}", value);
Console.ReadLine();
}
}


Using Methods with Parameters

Methods can also be declared with parameters. Consider
the example of declared a method with parameters:
void DisplayResult (int result)
{
//…..
}
When the methods are declared with parameters, they
should be called with parameters. The methods with
parameters are called by passing the value using the
following mechanism:
Value
Reference
Output


Using Methods with Parameters (Contd.)

• Value: The parameters passed by value creates a separate
copy in the memory. The following example shows the
parameters passed by value:
void CalculateSum( int num1, int num2)
{
//…
}
void Accept()
{
int val1=10;
int val2=2;
CalculateSum(val1,val2);
}



• Reference: The parameters passed by reference does not
creates a separate copy of the variable in the memory. A
reference parameter stores the memory address of the data
member passed. The following example shows the
parameters passed by reference:
void CalculateSum( ref int num1,ref int num2)
{
//…
}
void Accept()
{
int val1=10;
int val2=2;
CalculateSum( ref val1,ref val2);
}


• Output: The output parameters are used to pass the value
out of the method. The following example shows the
parameters passed by reference:
void CalculateSum( ref int num1,ref int num2, out
int result)
{
result=num1+num2;
}
void Accept()
{
int val1=10;
int val2=2;
int recieveVal;
CalculateSum( ref val1,ref val2,out
recieveVal);
}

Demo: Swapping Two Numbers by Using Methods with Parameters

Problem Statement:
Write a program to swap two numbers by using reference type
parameters in a method.


Summary

In this session, you learned that:
Abstraction is the process of reducing information content in
order to retain only the relevant information for a particular
purpose.
Encapsulation is the process of hiding all 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.
The public access specifier allows a class to expose 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 functions and
objects.


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 the private access specifier
while implementing inheritance.
A method is a set of one or more program statements that can
be executed by referring to the method name.
Defining a method means declaring the elements of its
structure.
The access modifiers that can be used with methods are
public, protected, internal, protected internal, and private.
Parameters allow information to be passed into and out of a
method. When you define a method, you can include a list of
parameters in parentheses.


Summary (Contd.)

Parameters can be passed by using any one of the following
parameters types:
• Value
• Reference
• Output
– Pass by value is the default mechanism for passing
parameters in C#.
– A reference parameter is a reference to a memory location of a
data member.
– Output parameters are like reference parameters, except that
they transfer data out of the method rather than into it.
– The return statement is used to return the control to the caller.


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