Understanding basic .NET OOPS concepts

2. • Introduction to OOPS
• Class and Object
• Encapsulation
• Inheritance
• Polymorphism
• Interfaces
• Delegate
• Access Modifiers
• Namespace
Agenda

3. About OOPS
OOPS is a programming language organized around objects (data) rather than action
and logic.
It is composed of self sufficient modules (“Class”), each instance (“Object”)
contains information to manipulate its data (“Members”)
Four main features of OOPS are
• Abstraction
• Encapsulation
• Polymorphism
• Inheritance

4. Object and Class
• Object is an instance of a class
• Object has state, behavior, and identity
• Object can be created by using the NEW keyword
• Communicates with other objects through message passing
Object
• It is a user defined data type
• In OOP you program a class as a template for a specific object
or groups ob objects that will always have the same features.
• Other types of classes
• Abstract class
• Static class
Class

5. Encapsulation
Encapsulation is the process of binding/wrapping
the data and methods into a single entity
Encapsulation is realized through the classes.
Encapsulation guarantees the integrity of the data
in the object
Three main parts of Object
• Interface
• Implementation or Behavior
• Member or Instance variables

6. Access modifiers
are used to
implement
encapsulation
It reduces system
complexity and
thus increases
robustness, by
limiting the
interdependencies
Abstraction is
achieved through
encapsulation
Object and
Properties are
examples for
encapsulation

7. Inheritance
Inheritance is a way to form new CLASSES using classes that have
already been.
Inheritance is employed to help REUSE existing code with little or no
modification.
The new classes, known as Sub-classes (or derived classes), inherit
attributes and behavior of the pre-existing classes, which are referred to
as Super-classes (or ancestor classes).
The inheritance relationship of SUB and SUPER CLASSES gives rise to a
HIERARCHY.

8. Inheritance
Purpose
• Reuse, extend, and modify the
behavior defined in other
classes
• Allows to build a hierarchy of
related classes
Only single inheritance is allowed
in .NET
Three types of inheritance
• Implementation
• Interface
• Visual
To avoid inheritance, we need to
use ‘sealed’ keyword

9. Polymorphism
Many forms of a single object is
called Polymorphism.
Polymorphism is important not
only to the derived classes, but
to the base classes as well.
It allows you to invoke methods
of derived class through base
class reference during runtime.
It has the ability for classes to
provide different
implementations of methods that
are called through the same
name.

10. Polymorphism Contd…
Polymorphism is of two types:
• Compile time polymorphism/Overloading
• Runtime polymorphism/Overriding
Compile Time Polymorphism
• Compile time polymorphism is method and operators
overloading. It is also called early binding.
• In method overloading method performs the
different task at the different input parameters.

11. Polymorphism Contd…
• Runtime time polymorphism is done
using inheritance and virtual
functions. Method overriding is
called runtime polymorphism. It is
also called late binding.
• When overriding a method, you
change the behavior of the method
for the derived class. Overloading
a method simply involves having
another method with the same
prototype.
When and why to use method
overloading ?
Runtime Time
Polymorphism

12. Function Overloading
Using same
name for
two or more
functions
Functions
should differ
with the
function
signature
Function
signature is
1.Number of
parameters
2.Different
data types of
parameters
3.Sequence of
parameters
Return type
is NOT part
of function
signature

13. Operator overloading
Using
• Static member
functions using the
operator keyword
Syntax
• <access modifier>
<Class Name>
operator <operator
symbol> (parameter
list)
• {
• .Do something
• }
Few types of
operator overloading
• Unary operator
overloading
• Binary operator
overloading

14. Abstract class
Purpose of an abstract class is to provide a common
definition of a base class
An abstract class cannot be instantiated
Abstract classes may also define abstract methods
Use abstract keyword
Abstract methods have no implementation
Use override keyword to implement abstract methods

15. Virtual members
Virtual members enable derived classes to extend a base class
Base class member should use virtual and derived class member should use
override
Fields cannot be virtual

16. Override virtual members in the base class
Inherit base class method without overriding it
Define new non-virtual implementation that hide the base class
implementations
The derived class can choose whether to

17. Interfaces
Interfaces describe a group of related functionalities
Interfaces are defined by using the INTERFACE keyword
Non-abstract type inheriting the interface must implement all its
members
Interfaces contain no implementation of methods
An interface cannot be instantiated directly

18. Interfaces Contd…
Classes can inherit from more
than one interface
An interface can itself inherit
from multiple interfaces
Interfaces members are
automatically public
The member of class
implementing interface member
must be of the following
• Public and non-static
• Same name and signature

19. Difference
Abstract Class Interface
Abstract class may contain concrete
methods
Interface contains methods that must
be abstract
Abstract class may contain non-public
members.
Members in an interface are public by
default
whereas abstract class is used to
"extends".
Interface is used to "implements";
Single inheritance Multiple inheritance
Abstract class can "extends" another
class and "implements" multiple
interfaces.
Interface can "extends" another
interface
One class can only "extends" one
super class
interface is more flexible than
abstract class because it "implements"
multiple interfaces.
Any class can extend an abstract
class.
only an interface can extend another
interface

20. Delegates

21. Delegates Contd…
Multi cast delegate
• Refer to multiple methods
of matching signature
• Derived from
System.MulticastDelegate
class
• Example: to call two
methods on a button click
event
Steps to use delegates
• Declare a delegate with a
function signature
• Instantiate the declared
delegate
• Use the delegate to
execute a function

22. Access Modifiers
All types and type members have
an accessibility level
which controls whether they can
be used from other code in your
assembly or other assemblies.
Access modifiers are
determined by the scope of
visibility for variables and
methods.
Used to implement encapsulation
and abstraction

23. Access Modifiers
Types of access
modifiers
• private
• public
• protected
• internal
• internal
protected
Default access
modifier for class
is internal
Default access
modifier for data
member is private

24. Namespace
The namespace keyword is used to declare a scope.
This namespace scope lets you organize code and
gives you a way to create globally unique types.
Within a namespace, you can declare one or more of the following types:
1.another namespace
2.class
3.interface
4.struct
5.enum
6.Delegate

25. namespace Name1
{
class A {}
}
namespace Name2
{
class A {}
}
We can also use nested namespace
namespace csharp_example
{
// Program start class
class NamespaceCE
{
// Main begins program execution.
public static void Main()
{
// Write to console
Console.WriteLine("This is the new C# Example Namespace.");
}
}
}
Namespace Example