C# OOPS Interview Questions – Freshers & Experienced Guide

Introduction to C# OOPS

C# OOPS (Object-Oriented Programming System) is a programming paradigm that organizes code using objects and classes. It is based on four main pillars: Abstraction, Encapsulation, Inheritance, and Polymorphism.

Abstraction in C#

Abstraction hides implementation details and exposes only essential functionality. It is implemented using abstract classes and interfaces.

public abstract class PaymentProcessor
{
    public abstract void ProcessPayment(decimal amount);
}

Polymorphism in C#

Polymorphism allows objects to take multiple forms. Two types in C#:

• Compile-time Polymorphism: Method & Operator Overloading
• Runtime Polymorphism: Method Overriding & Interfaces

Real Project Example – Singleton Pattern

public class Logger
{
    private static Logger _instance;
    private Logger() {}
    public static Logger Instance => _instance ??= new Logger();
}

✔ Ensures single instance
✔ Global access point
✔ Used in logging, config, DB connections

Access Modifiers in C#

public, private, protected, internal, protected internal

public class Example
{
    private int x;
    protected int y;
    internal int z;
}

Constructors in C#

Special methods to initialize objects. Types: Default, Parameterized, Copy, Static, Private

Abstract Class vs Interface

Abstract class: Can have abstract & non-abstract methods, fields. Interface: Only method signatures, multiple inheritance supported.

Frequently Asked Questions – C# OOPS