OOP Using C# Guide

Object-Oriented Programming Using C#
Objectives

In this session, you will learn to:
Implement constructors
Implement destructors
Identify the life cycle of an object
Describe polymorphism
Implement function overloading
Identify need for operator overloading

Ver. 1.0 Session 8 Slide 1 of 24

Implementing Constructors

A constructor is a special type of method that is invoked
when you create a new instance of a class.
A constructor is used to initialize the members of the class.
The name of a constructor is the same as the name of the
class that contains it.


The Need of Constructors

A constructor is special member function within the
class which is executed when an object of the class is
created.


Types of Constructors

The two types of constructors are:
– Instance constructors: They are called whenever an instance
of a class is created. These constructors are used to initialize
the data members of the class.
– Static constructors: They are used to initialize the static
variables of a class. These variables are created using static
keyword and they store values that can be shared by all the
instances of a class.


Constructors with Parameters

A constructor can be modified to accept the user-supplied
values at run time.
Objects can be initialized using the default constructor with
values hard-coded in the program. But there might be a
requirement where the variables need to be initialized with
user supplied values.


Implementing Destructors

Destructors are special methods that are used to release
the instance of a class from memory.
A class can have only one destructor.
The purpose of the destructor is to perform the required
memory cleanup action.
The .NET Framework automatically runs the destructor to
destroy objects in the memory.


Declaration of Destructors

A destructor has the same name as its class but is prefixed
with a ~ , which is the symbol of tilde.
Destructors cannot be inherited or overloaded.
Garbage collection is a process that automatically frees the
memory of objects that are no more in use.
The decision to invoke the destructor is made by a special
program of C# known as the garbage collector.
The process of garbage collection happens automatically. It
ensures that:
Objects get destroyed
Only unused objects are destroyed


Declaration of Destructors (Contd.)

C# provides the following methods to release the instance
of a class from memory:
– Finalize(): It is a special method that is called from the class to
which it belongs or from the derived classes. The Finalize()
destructor is called after the last reference to an object is
released from the memory.
– Dispose(): This method is called to release a resource, such
as a database connection, as soon as the object using such a
resource is no longer in use. The IDisposable interface
contains the Dispose() method. Therefore, to call the
Dispose() method, the class must implement the
IDisposable interface.


Identifying the Life Cycle of an Object

Let us understand the life cycle of an object with the help of
the following code:
using System;
//Life Cycle of an Object
namespace Objects
{
class TestCalculator
{
TestCalculator()
{
Console.WriteLine("Constructor Invoked");
}


Identifying the Life Cycle of an Object (Contd.)

~TestCalculator() The destructor of all
{ the object is invoked
Console.WriteLine when the garbage
("Destructor Invoked"); collector is invoked.
}
public static void The Calc1 object has
Main(string[] args) function scope.
{ Therefore, its
Console.WriteLine("Main() constructor is executed
Begins"); after the execution of
TestCalculator Calc1 = Main() begins.
new TestCalculator();


Identifying the Life Cycle of an Object (Contd.)

~Console.WriteLine("Inner Block The Calc2 object has
Begins "); block scope.
TestCalculator Calc2 = new Therefore, its
TestCalculator(); constructor is executed
after the inner block
Console.WriteLine("Inner Block begins.
Ends");
}
Console.WriteLine("Main() ends");

}

}
}


Introducing Polymorphism

In Object-Oriented Programming (OOPs), polymorphism
allows one interface to be used for multiple functions.
Polymorphism reduces the complexity within the functions
of a class of a program.
Polymorphism can either be static or dynamic.


Static Polymorphism

Static polymorphism refers to an entity, which exists in
various forms simultaneously.
C# uses two approaches to implement static polymorphism.
These are:
– Function overloading: This approach allows using the same
name for two or more functions. Each redefinition of a function
must use different types of parameters, sequence of
parameters, or a number of parameters.
– Operator overloading: This approach allows user-defined
types such as structures and classes, to use overloaded
operators for easy manipulation of their objects.


Dynamic Polymorphism

In dynamic polymorphism, the decision about function
execution is made at run time.
Dynamic polymorphism is more useful than static
polymorphism as it provides much more flexibility for
manipulating the objects.
C# uses two approaches to implement dynamic
polymorphism:
– Abstract classes: Are the special type of base classes that
consist of abstract class members.
– Virtual functions: Are the functions that do not really exist,
however, appear to be present in some parts of the program.


Implementing Function Overloading

Function overloading is implemented by defining two or
more functions in a class sharing the same name.
In function overloading, each definition of a function must
differ in its function signature.


Function Signature

The signature of a function is defined by:
– The number of parameters
– The data types of parameters
– The sequence of the parameters


Constructor Overloading

Constructors can also be parameterized, and therefore,
they can be overloaded.
Overloaded constructors are commonly used in C# to
provide flexibility while creating an object.


Demo: Displaying Days Using Function Overloading

Problem Statement:
Tim has to develop a software application for a primary school.
The application should accept the month entered by the
student and display the total number of days of that month.


Demo: Displaying Days Using Function Overloading (Contd.)

Solution:
To develop the required application, Tim needs to perform the
following tasks:
1. Create a console-based application.
2. Build and execute an application.


Operator Overloading

Operator overloading provides additional capabilities to C#
operators when they are applied to user-defined data types.
Only the predefined set of C# operators can be overloaded.


Need for Operator Overloading

To use operators with user-defined data types, they need to
be overloaded according to a programmer’s requirement.
The following table describes the overload ability of the
operators in C#.
Operators Description

+, -, ! , ~, ++ , -- These unary operators take one operand and can be
overloaded.
+, -, * , /, % These binary operators take two operands and can be
overloaded.
==, !=, <, >, <=, >= The comparison operators can be overloaded.

&&, || The conditional logical operators cannot be overloaded
directly, but they are evaluated using & and | which can be
overloaded.
+=, -=, *=, /=, %= The assignment operators cannot be overloaded.
=, ., ?:, ->, new, is, These operators cannot be overloaded.
sizeof, typeof


Summary

In this lesson, you learned that:
Constructors are member functions of a class and are invoked
when an instance of the class to which they belong is created.
A constructor has the same name as its class.
A destructor is invoked when any instance of a class ceases to
exist.
A destructor has the same name as its class, but it is prefixed
with a ~ (tilde).
Constructors are special methods that allow control over the
initialization of objects.
Destructors are special methods that are used to release the
instance of a class from memory.
Garbage collection is a process that automatically frees the
memory of objects that is no more in use.


Summary (Contd.)

– The Finalize() destructor is called after the last reference
to an object is released from the memory.
– The Dispose() method is called to release a resource, such
as a database connection, when the object using such a
resource is no longer in use.
– The term polymorphism has been derived form the Greek
words ‘poly’ and ‘morphos’, which mean ‘many’ and ‘forms’,
respectively.
– Polymorphism allows one interface to be used for multiple
functions.
– Static polymorphism refers to an entity, which exists in different
forms simultaneously.
– In dynamic polymorphism, the decision about function
execution is made when code is executed.


Summary (Contd.)

Function overloading is the process of using the same name
for two or more functions in a class.
The number, type, or sequence of parameters of a function is
called its function signature.
Overloaded constructors are commonly used in C# to provide
flexibility while creating an object.
Operator overloading provides additional capabilities to C#
operators when they are applied to user-defined data types.
The predefined C# operators can be overloaded by using the
operator keyword.
Operators may be considered as functions internal to the
compiler.


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