Introduction to Object Oriented Programming Concepts

Object Oriented Programming(OOP) Features

Object oriented programming (OOP) is a programming model where programs are organized around object and data rather than action and logic.
OOP allows decomposition of a problem into a number of entities called Object and then builds data and function around these objects.
The program is divided into a number of small units called Object. The data and function are build around these objects.
The data of the objects can be accessed only by the functions associated with that object.
The functions of one object can access the functions of other object.

OOP has the following important features:

Class

A class is the core of any modern Object Oriented Programming language such as C#.
In OOP languages, it is a must to create a class for representing data.
Class is a blueprint of an object that contains variables for storing data and functions to performing operations on these data.
Class will not occupy any memory space and hence it is only a logical representation of data.
To create a class, you simply use the keyword "class" followed by the class name:

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class Employee
{

}

Object

Objects are the basic run-time entities in an object oriented system. They may represent a person, a place or any item that the program has to handle.
"Object is a Software bundle of related variable and methods. "
“Object is an instance of a class.”

Class will not occupy any memory space. Hence to work with the data represented by the class, you must create a variable for the class, which is called as an object.
When an object is created by using the keyword new, then memory will be allocated for the class in heap memory area, which is called as an instance and its starting address will be stored in the object in stack memory area.
When an object is created without the keyword new, then memory will not be allocated in heap, i.e., instance will not be created and object in the stack contains the value null.
When an object contains null, then it is not possible to access the members of the class using that object.

class Employee
{

}

Syntax to create an object of class Employee:

Employee objEmp = new Employee();

All the programming languages supporting object oriented programming will be supporting these three main concepts:

Encapsulation
Inheritance
Polymorphism

Abstraction

Abstraction is "To represent the essential feature without representing the background details."
Abstraction lets you focus on what the object does instead of how it does it.
Abstraction provides you a generalized view of your classes or object by providing relevant information.
Abstraction is the process of hiding the working style of an object, and showing the information of an object in an understandable manner.

Real World Example of Abstraction

Suppose you have an object Mobile Phone.
Suppose you have 3 mobile phones as follows:

Nokia 1400 (Features:- Calling, SMS)
Nokia 2700 (Features:- Calling, SMS, FM Radio, MP3, Camera)
Black Berry (Features:-Calling, SMS, FM Radio, MP3, Camera, Video Recording, Reading E-mails)

Abstract information (Necessary and Common Information) for the object "Mobile Phone" is to make a call to any number and can send SMS." so that, for mobile phone object you will have an abstract class like the following:

    abstract class MobilePhone
    {
        public void Calling();
        public void SendSMS();
    }

    public class Nokia1400 : MobilePhone
    {

    }

    public class Nokia2700 : MobilePhone
    {
        public void FMRadio();
        public void MP3();
        public void Camera();
    }

    public class BlackBerry : MobilePhone
    {
        public void FMRadio();
        public void MP3();
        public void Camera();
        public void Recording();
        public void ReadAndSendEmails();
    }

Abstraction means putting all the variables and methods in a class which is necessary.
For example: Abstract class and abstract method.
Abstraction is the common thing.

Examples

If somebody in your college tells you to fill an application form, you will fill your details like name, address, data of birth, which semester, percentage you got, etc.
If some doctor gives you an application to fill the details, you will fill the details like name, address, date of birth, blood group, height and weight.

See in the above examples what is the common thing?
Age, name, address so you can create the class which consists of the common thing that is called abstract class.
That class is not complete and it can be inherited by another class.

Encapsulation

Wrapping up data member and method together into a single unit (i.e. Class) is called Encapsulation.
Encapsulation is like enclosing in a capsule. That is enclosing the related operations and data related to an object into that object.
Encapsulation is like your bag in which you can keep your pen, book, etc. It means this is the property of encapsulating members and functions.

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    class Bag
    {
        book;
        pen;
        ReadBook();
    }

Encapsulation means hiding the internal details of an object, i.e., how an object does something.
Encapsulation prevents clients from seeing its inside view, where the behaviour of the abstraction is implemented.
Encapsulation is a technique used to protect the information in an object from the other object.
Hide the data for security such as making the variables as private, and expose the property to access the private data which would be public.
So, when you access the property, you can validate the data and set it.

Example

class Demo
{
   private int _mark;

   public int Mark
   {
     get { return _mark; }
     set { if (_mark > 0) _mark = value; else _mark = 0; }
   }
}

Real World Example of Encapsulation

Let's take an example of Mobile Phone and Mobile Phone Manufacturer.
Suppose you are a Mobile Phone Manufacturer and you designed and developed a Mobile Phone design(class), now by using machinery you are manufacturing a Mobile Phone(object) for selling, when you sell your Mobile Phone, the user only learns how to use the Mobile Phone but not how this Mobile Phone works.
This means that you are creating the class with function and by making object (capsule) of it, you are making availability of the functionality of your class by that object and without the interference in the original class.

Example 2

TV operation
It is encapsulated with cover and we can operate with remote and no need to open TV and change the channel.
Here everything is in private except remote so that anyone can access not to operate and change the things in TV.

ENCAPSULATION:- Encapsulation provides the ability to hide the internal details of an object from its users.The concept of encapsulation is also known as data hiding or information hiding. In c# , Encapsulation is implemented using the access modifier keywords.

Public
Private
protected
Internal
Protected Internal

Inheritance

When a class acquire the property of another class, it is known as inheritance.
Inheritance is the process of object reusability.
For example: A child acquires the property of parents.

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public class ParentClass
    {
        public ParentClass()
        {
            Console.WriteLine("Parent Constructor.");
        }

        public void print()
        {
            Console.WriteLine("I'm a Parent Class.");
        }
    }

    public class ChildClass : ParentClass
    {
        public ChildClass()
        {
            Console.WriteLine("Child Constructor.");
        }

        public static void Main()
        {
            ChildClass child = new ChildClass();

            child.print();
        }
    }

Output

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Parent Constructor. 
Child Constructor. 
I'm a Parent Class.

Polymorphism

Polymorphism means one name many forms.
One function behaves in different forms.
In other words, "Many forms of a single object is called Polymorphism."

Real World Example of Polymorphism

Example 1

A Teacher behaves with his student.
A Teacher behaves with his/her seniors.
Here teacher is an object but attitude is different in different situations.

Example 2

Person behaves like a SON in the house, at the same time that person behaves like an EMPLOYEE in office.

Example 3

Your mobile phone, one name but many forms:

As phone
As camera
As mp3 player
As radio

Polymorphism in .NET

Difference between abstraction and encapsulation is as given in the table below:

Abstraction	Encapsulation
1. Abstraction solves the problem in the design level.	1. Encapsulation solves the problem in the implementation level.
2. Abstraction is used for hiding the unwanted data and giving relevant data.	2. Encapsulation means hiding the code and data into a single unit to protect the data from outside world.
3. Abstraction lets you focus on what the object does instead of how it does it.	3. Encapsulation means hiding the internal details or mechanics of how an object does something.
4. Abstraction- Outer layout, used in terms of design. For example: Outer Look of a Mobile Phone, like it has a display screen and keypad buttons to dial a number.	4. Encapsulation - Inner layout, used in terms of implementation. For example: Inner Implementation detail of a Mobile Phone, how keypad button and Display Screen are connect with each other using circuits.

The easier way to understand Abstraction and encapsulation is as follows:

Real World Example

Take an example of mobile phone:
You have a mobile phone, you can dial a number using keypad buttons. Even you don't know how these are working internally. This is called abstraction. You have the only information that is needed to dial a number. But not its internal working of mobile.
But how the mobile phone works internally and how keypad buttons are connected with internal circuit is called encapsulation.

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