Object Oriented Programming with C#

Created By-

PRANAB BHATTACHARYA
MCA-TY
Roll no. : 14

 Overview
 Classes and objects

Class members

Methods

Constructors

Destructors

Nested Classes

Access Modifiers and Access levels

Static (Shared) Classes and Members

Anonymous types
 Inheritance

Overriding members
• Sealed and Abstract classes
 Interfaces
1

o .NET

Framework languages provide full support for
Object-oriented programming
o Encapsulation, Inheritance, Polymorphism
o Encapsulation means that a group of related
properties, methods, and other members are treated as a
single unit or object.
o Inheritance describes the ability to create new
classes based on an existing class.
o Polymorphism means that you can have multiple
classes that can be used interchangeably, even though
each class implements the same properties or methods
in different ways.

2

o Classes describe the type of objects…
o …while objects are usable instances of classes.
o Using the blueprint analogy, a class is a
blueprint, and an object is a building made from
that blueprint.
To define a class and object:
class SampleClass
{
}
SampleClass SC1 = new SampleClass();
3

o A method is an action that an object can perform.
To define a method of a class:
class SampleClass
{
public int sampleMethod(string sampleParam)
{
// Insert code here
}
}
4

o A class can have several implementations, or
overloads, of the same method that differ in the
number of parameters or parameter types.
oTo overload a method:
public int sampleMethod(string sampleParam) {};
public int sampleMethod(int sampleParam) {}
Public int sampleMethod(int param1,int param2){};
o In most cases you declare a method within a class
definition. However, both Visual Basic and C# also
support extension methods that allow you to add
methods to an existing class outside the actual

5

o Constructors are class methods that are executed
automatically when an object of a given type is created. (Run
before any other code)
o Constructors usually Initialize the data members.
oSupport Overloading.

To define a constructor for a class:
public class SampleClass
{
int I;
public SampleClass()
{
I = 1;
}

6

o Destructors are used to destruct instances of classes.
o In the .NET Framework, the garbage collector
automatically manages the allocation and release of
memory for the managed objects in your application.
o Destructors are still needed to clean up any
unmanaged resources that your application creates.
o There can be only one destructor for a class.
7

o A class defined within another class is called nested.
(Default - private)
class Container
{
class Nested
{
// Add code here.
}
}

o To create an instance of the nested class, use the name
of the container class followed by the dot and then
followed by the name of the nested class:
Container.Nested nestedInstance = new

8

o All classes and class members can specify what access level
they provide to other classes by using access modifiers.
The following access modifiers are available:
C# Modifier
Definition
___________________________________________________
Public
The type or member can be accessed by any other
code in
the same assembly or another assembly that
references it.
Private
The type or member can only be accessed by code
in the
same class.
Protected The type or member can only be accessed by code
in the
same class or in a derived class.
Internal
The type or member can be accessed by any
code in the

9

o A static member of the class is a
property, procedure, or field that is shared by all
instances of a class.
o To define a static (shared) member:
static class SampleClass
{
public static string SampleString = "Sample
String";
}

10

o To access the static member, use the name of the
class without creating an object of this class:
Console.WriteLine(SampleClass.SampleStrin
g);
o Static (shared) classes in C# have static (shared)
members only and cannot be instantiated.
o Static (shared) members also cannot access nonstatic (non-shared) properties, fields or methods
11

o Enable you to create objects without writing a class
definition for the data type. (compiler generates a
class)
oThe class has no usable name and contains the
properties you specify in declaring the object.
o To create an instance of an anonymous type:
// sampleObject is an instance of a simple anonymous
type.
var sampleObject =
new { FirstProperty = "A", SecondProperty = "B" };

12

o Creates a new class that reuses, extends, and modifies
the behavior that is defined in another class.
Base Class
– The class whose members are
inherited
Derived Class – The class that inherits those
members.
o In C#, all classes implicitely inherit from the Object
class.
* .NET Framework doesn’t support MULTIPLE
INHERITANCE i.e. One derived class can not have more
than One base class
Syntax :

13

o By default all classes can be inherited.
o We can specify whether a class must not be used as a
base class, or create a class that can be used as a base
class only.
To specify that a class cannot be used as a base class:
public sealed class A { }

 To specify that a class can be used as a base class
only and cannot be instantiated :
public abstract class B { }

14

o By default, a derived class inherits all members
from its base class.
oyou want to change the behavior of the inherited
member, you need to override it
oWhat is Overriding ??
-> Overriding is defining a new implementation of a
method, property or event in the derived class.
15

Overriding modifiers..
C# Modifier
Definition
virtual (C# Reference) - Allows a class member to be
overridden in a derived class.
override (C# Reference) - Overrides a virtual
(overridable) member defined in the base class.
abstract (C# Reference) - Requires that a class member
to be overridden in the derived class.

16

o Interfaces, like classes, define a set of
properties, methods, and events.
o But unlike classes, interfaces do not provide
implementation.
oThey are implemented by classes, and defined
as separate entities from classes.

oAn interface represents a contract, in that a
class that implements an interface must
implement every aspect of that interface exactly

17

o To define an interface:
interface ISampleInterface
{
void doSomething();
}

o To implement an interface in a class:
class SampleClass : ISampleInterface
{
void ISampleInterface.doSomething()
{
// Method implementation.
}
}

18

Object Oriented Programming with C#

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