Introduction

In this lesson, you will learn OOP concepts in C# for beginners with clear explanations and examples. Object-Oriented Programming helps you build clean, reusable, and scalable applications.

What is OOP?

OOP (Object-Oriented Programming) is a way of writing programs using classes and objects. It models real-world entities like Car, Student, or BankAccount.

1. Class and Object

A class is a blueprint. An object is an instance of that class.

class Car
{
    public string color = "Red";
}

class Program
{
    static void Main()
    {
        Car car1 = new Car();
        Console.WriteLine(car1.color);
    }
}

Explanation

• Class defines properties/behavior
• Object uses the class to access data

2. Encapsulation (Data Hiding)

Encapsulation means protecting data and exposing it using methods or properties.

class Person
{
    private string name;

    public void SetName(string n)
    {
        name = n;
    }

    public string GetName()
    {
        return name;
    }
}

Why use it?

• Protect data
• Control access
• Improve security

3. Inheritance (Code Reuse)

Inheritance allows one class to use properties and methods of another class.

class Animal
{
    public void Speak()
    {
        Console.WriteLine("Animal speaks");
    }
}

class Dog : Animal
{
}

Benefits

• Code reuse
• Cleaner structure
• Less duplication

4. Polymorphism (Many Forms)

Polymorphism allows the same method to behave differently.

Method Overloading

class Math
{
    public int Add(int a, int b)
    {
        return a + b;
    }

    public int Add(int a, int b, int c)
    {
        return a + b + c;
    }
}

Method Overriding

class Animal
{
    public virtual void Sound()
    {
        Console.WriteLine("Animal sound");
    }
}

class Dog : Animal
{
    public override void Sound()
    {
        Console.WriteLine("Dog barks");
    }
}

5. Abstraction (Hide Complexity)

Abstraction hides complex implementation and shows only essential features.

abstract class Vehicle
{
    public abstract void Start();
}

class Car : Vehicle
{
    public override void Start()
    {
        Console.WriteLine("Car starts");
    }
}

Use case

• Show only required functionality
• Hide internal logic

Real-World Example

Think of a Bank Account system:

• Class: BankAccount
• Encapsulation: balance is private
• Inheritance: SavingsAccount, CurrentAccount
• Polymorphism: different interest calculation

Key Points

• Class and Object are the base of OOP
• Encapsulation protects data
• Inheritance enables reuse
• Polymorphism provides flexibility
• Abstraction hides complexity

Internal Links

• Course Page: .NET Course for Beginners