Object-oriented programming (OOP) is a paradigm that splits programs into objects that contain both data and functions. Classes define the attributes and behaviors of objects. Objects are instances of classes that encapsulate their state and behavior. Key concepts of OOP include inheritance, abstraction, polymorphism, and encapsulation.

1. Focused more for interview Perspective and Easy Understanding

2.  Object-Oriented Programming (OOP) is a
software development paradigm that
suggests developers to split a program in
building blocks known as objects.
 The OOP paradigm allows developers to
define the object's data, functions, and its
relationship with other objects.

3.  Code Reusability
 Enables to model real world object
 Easy Modification
 Easy Maintenance
 More Flexible

4.  Defines an Abstract thing of a thing (i.e.
Object)
 Explaining its Behavior
 A user-defined data structure that groups
properties and methods.
 Class doesn’t occupies memory.
 Class is a definition
 Abstract classes are classes that can have no
instances

5.  A Single entity Which holds Data and Method.
 It’s Structure.
 Should be understandable by a non-
Programmer
DOG
(Class)
Color, Shape
(Characteristic)
Bark, Pee, Run
(Behaviors)
Members
Abstract characteristics
of a thing
Fields - _Color
Properties - Color
Fields - _Color
Properties - Color

6.  Specify Class Name
 Declare Data members
 Declare Methods
 Define the Processing

7. Program them in the following order:
 Namespace: The namespace is a keyword that
defines a distinctive name or last name for the
class. A namespace categorizes and organizes the
library (assembly) where the class belongs and
avoids collisions with classes that share the same
name.
 Class declaration: Line of code where the class
name and type are defined.
 Fields: Set of variables declared in a class block.

8.  Constants: Set of constants declared in a class
block.
 Constructors: A method or group of methods
that contains code to initialize the class.
 Properties: The set of descriptive data of an
object.
 Events: Program responses that get fired
after a user or application action.
 Methods: Set of functions of the class.

9.  Destructor: A method that is called when the
class is destroyed.
 In managed code, the Garbage Collector is in
charge of destroying objects; however, in some
cases developers need to take extra actions when
objects are being released, such as freeing
handles or de-allocating unmanaged objects.
 In .NET, there is no concept of deterministic
destructors. The Garbage Collector will call the
Finalize() method at a non-deterministic time
while reclaiming memory for the application.

11. Access keywords
 Access keywords define the access to class
members from the same class and from other
classes. The most common access keywords are:
 Public: Allows access to the class member from
any other class.
 Private: Allows access to the class member only
in the same class.
 Protected: Allows access to the class member
only within the same class and from inherited
classes.

12.  Internal: Allows access to the class member
only in the same assembly.
 Protected internal: Allows access to the class
member only within the same class, from
inherited classes, and other classes in the
same assembly. Static: Indicates that the
member can be called without first
instantiating the class.

13.  A particular Instance of a Class
 Objects are the building blocks of OOP
 Represent real world things in an abstract way
 Commonly defined as variables or data
structures that encapsulate behavior and data
in a programmed unit
 The objects will all act as independent units in
their own right, and they will be responsible
for carrying out a certain process

14.  Object identity:
 Every object is unique and can be differentiated from
other objects. Each time and object is created
(instantiated) the object identity is defined.
 Object behavior:
 What the object can do. In OOP, methods work as
functions that define the set of actions that the object
can do.
 Object state:
 The data stored within the object at any given
moment. In OOP, fields, constants, and properties
define the state of an object.

15.  Inheritance
 Abstraction
 Polymorphism
 Encapsulation
 Event

16.  Is like inheriting the abstract characteristics from
other class - It is a kind of hierarchy
 Base Class will be inherited to derived class
 is a way to form new classes using classes that
have already been defined
 is-a relationships represent a hierarchy between
classes of objects
 Use:
 Reuse of Code – uses the attributes of the base class
 Extensibility – Has it’s own Attributes
.Net Inheritance Concepts
March 15, 2004
Brian Berejik
Matt Jackson
Vinnie Alwani

17.  Simple / Single
 Multilevel
 Hierarchical
 Multiple
 Hybrid

18.  Superclass: Parent class
 Subclass: Child class
 Base class: Parent class
 Derived class: Child class

19.  Is like inheriting from more than one base
class.
 .Net do not allow. But using Multiple interface
inheritance this can be achieved.

20.  Information Hiding
 Visibility to the methods and not to the fields
 E.g. A Report designer for a programmer
 Packs the data and Method and protects from
external tampering
 Exposing only the details that are relevant: the
public interface
 Improves Security

21.  Protected cName as string
Protected Function ChangeName(NewName)
Me.cName = NewName
End Function

22.  As we cannot hide entire object we give access
to some specific part of data.
 Conceptual boundaries of an object
 Focuses on the essential characteristics of an
object
 a named entity made up of selected attributes
and behavior specific to a particular usage of
the originating entity
 Improves Security
For example see notes below

23.  One entity existing in multiple forms
 Behavior depends on the type of data
 Same message to diff objects results in
different behavior
 Linked to inheritance and assures that derived
class to override the implementation of
parents methods.

24.  Class Employee
Function PayEmployee()
PayEmployee = Hours * HourlyRate
End Function
 Class CommissionedEmployee
Inherits Employee
Overrides Function PayEmployee()
PayEmployee = BasePay + Commissions
End Function

25.  Upcasting
Casting an object of any type to another type
which is above it in the inheritance hierarchy.
 Downcasting
Casting an object of any type to another type
which is below it in the inheritance hierarchy.
Example
 Sealed Class
When applied to a class, the sealed modifier prevents
other classes from inheriting from it.

26.  static classes and static methods are used to create
data and functions that can be accessed without
creating an instance of the class.
class CompanyInfo {
public string GetCompanyName() { return "CompanyName"; }
public string GetComAddress() { return "ComAddress"; }
 These methods do not need to be attached to a
specific instance of the class. Therefore, instead of
creating unnecessary instances of this class, you can
declare it as a static class, like this:
static class CompanyInfo {
public static string GetCompanyName() {return "CompanyName";}
public static string GetComAddress() {return "ComAddress";}

27.  www.c-sharpcorner.com
 www.csharpcorner.com 2
 www.kuro5hin.org
 www.informit.com
 www.forums.asp.net
 www.developerfusion.com
 www.msdn.microsoft.com