⭐ Top 50 .NET Interview Questions and Answers (Fully Explained) (Perfect for Freshers + Experienced .NET Developers)-2025

 1. What is .NET Framework?

Answer:
.NET Framework is a Microsoft software development platform used to build Windows, Web, and Enterprise applications. It includes:

• CLR (Common Language Runtime)

• BCL (Base Class Library)

• Languages: C#, VB.NET, F#

• Tools: Visual Studio

It allows cross-language interoperability and simplifies memory management via the CLR.

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2. What is .NET Core / .NET 5+?

Answer:
.NET Core (now unified under .NET 5, .NET 6, .NET 7, .NET 8) is:

• Cross-platform (Windows, Linux, macOS)

• Open-source

• High-performance and lightweight

• Supports microservices, containers, and cloud-native apps

It replaced the old .NET Framework with a unified modern platform.

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3. What is the CLR?

Answer:
CLR (Common Language Runtime) is the runtime environment of .NET.
It handles:

• Memory management

• Garbage Collection

• Thread management

• Exception handling

• Code execution

• Security

It converts MSIL (Microsoft Intermediate Language) into native machine code.

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4. What is the difference between .NET Framework and .NET Core?

Answer:

Feature	.NET Framework	.NET Core/.NET 6+
Platform	Windows-only	Cross-platform
Open Source	Limited	Fully open-source
Performance	Moderate	High-performance
Deployment	System-level	Side-by-side
Architecture	Monolithic	Modular

.NET Core is recommended for modern applications, cloud applications, and microservices.

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5. What is C#?

Answer:
C# (C Sharp) is an object-oriented programming language developed by Microsoft.
Features:

• Strongly typed

• OOP-based

• Garbage-collected

• Supports LINQ, async/await, generics

• Used for web, desktop, API, game development (Unity), cloud apps.

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6. What is MSIL/IL Code?

Answer:
MSIL (or IL) is the intermediate code generated after compiling C# code.
CLR converts IL to native code using JIT (Just-In-Time) compiler.

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7. What is JIT Compiler?

Answer:
JIT Compiler converts MSIL into machine code during program execution.
Types of JIT:

• Pre-JIT

• Econo-JIT

• Normal JIT

This improves performance and optimizes based on runtime.

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8. What is OOPS in C#?

Answer:
OOPS stands for:

• Encapsulation

• Abstraction

• Inheritance

• Polymorphism

It helps create modular, maintainable, and reusable code.

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9. Explain Encapsulation with example.

Answer:
Encapsulation hides internal object details and exposes only required functionality.

Example:

public class BankAccount 
{
    private decimal balance;

    public void Deposit(decimal amount) => balance += amount;

    public decimal GetBalance() => balance;
}

Here, balance is protected from direct access.

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10. What is Inheritance in C#?

Answer:
Inheritance allows one class to inherit properties and methods of another.

Example:

class Car { public void Drive() {} }
class BMW : Car { }

BMW inherits Drive().

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11. What is Polymorphism?

Answer:
Polymorphism allows methods to behave differently based on runtime objects.

Example:

public virtual void Message() { }
public override void Message() { }

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12. Difference between Abstract Class and Interface.

Answer:

Abstract Class	Interface
Can have fields	No fields
Can have constructors	No constructors
Supports abstract + concrete methods	Only abstract methods
Single inheritance only	Multiple inheritance

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13. What are Value Types and Reference Types?

Answer:

• Value types: stored in stack → int, double, struct

• Reference types: stored in heap → class, array, string

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14. What is Boxing and Unboxing?

Answer:
Boxing: Converting value type → object (heap)
Unboxing: Converting object → value type

Example:

int x = 10;
object obj = x; // Boxing
int y = (int)obj; // Unboxing

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15. What is ASP.NET Core?

Answer:
A high-performance, cross-platform framework for building:

• Web apps

• REST APIs

• Microservices

• Cloud applications

Uses Middleware and Dependency Injection by default.

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16. What are Middleware components?

Answer:
Middleware is a pipeline that handles HTTP requests in sequence.
Examples:

• Authentication

• Routing

• Exception handling

• Logging

Implemented like:

app.UseMiddleware<CustomMiddleware>();

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17. What is Dependency Injection (DI)?

Answer:
A design pattern where dependencies are injected instead of being created inside classes.

Example:

services.AddScoped<IEmployeeService, EmployeeService>();

Benefits:

• Testability

• Loose coupling

• Readability

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18. What is Entity Framework Core?

Answer:
EF Core is an ORM (Object Relational Mapper) for .NET used to interact with databases using C# instead of SQL.

Features:

• Migrations

• LINQ queries

• Change tracking

• Database-first & Code-first support

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19. What is Code-First approach?

You create C# classes → EF creates database tables automatically.

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20. What is Database-First approach?

Database already exists → EF generates models and DbContext.

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21. What is Migration in EF Core?

Answer:
Migrations track database schema changes.

Commands:

Add-Migration Init
Update-Database

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22. What is LINQ?

Answer:
Language Integrated Query to perform queries on objects, collections, datasets, and DB.

Example:

var data = list.Where(x => x.Age > 20);

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23. What is async and await?

Answer:
Used for asynchronous programming to avoid thread blocking.

Example:

await Task.Delay(1000);

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24. What is Garbage Collection in .NET?

Answer:
Automatic memory management that frees unused objects.

Generations:

• Gen 0

• Gen 1

• Gen 2

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25. What is IDisposable Interface?

Used to release unmanaged resources manually.

Example:

using(var conn = new SqlConnection()) { }

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26. What is a Constructor and Destructor?

Constructor → initializes object
Destructor → frees resources (rare in .NET)

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27. What is Singleton Pattern?

Ensures only one instance of a class exists.

Example:

public static readonly Singleton Instance = new Singleton();

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28. What is Routing in ASP.NET Core?

Matches incoming HTTP requests to endpoints.

Example:

app.MapControllerRoute("default", "{controller}/{action}/{id?}");

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29. What is Model Binding?

ASP.NET Core automatically maps request data to parameters or models.

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30. What is ViewModel?

A DTO used between View and Controller to avoid exposing domain models.

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31. What is REST API?

Architectural style for building stateless, resource-based web services.

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32. Difference between GET and POST.

GET → Fetch data (idempotent)
POST → Create data (not idempotent)

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33. What is JWT Token?

A secure token used for authentication between client and server.
Parts:

• Header

• Payload

• Signature

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34. What is Swagger?

API documentation and testing tool built on OpenAPI specification.

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35. What is Microservices Architecture?

Application broken into independent services.
Benefits: scalability, fault isolation, cloud readiness.

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36. What is Kestrel?

The built-in high-performance web server in ASP.NET Core.

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37. What is Configuration in ASP.NET Core?

Manages app settings using:

• appsettings.json

• Environment variables

• Azure Key Vault

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38. What is CORS?

Cross-Origin Resource Sharing → Allows frontend apps to access APIs from other domains.

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39. What is a NuGet Package?

Dependency manager for .NET libraries.

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40. What is .NET Standard?

A versioned set of APIs available across all .NET platforms.

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41. Explain Sealed Class.

Cannot be inherited, used for security/performance.

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42. What is a Partial Class?

A class split into multiple files.

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43. What is Reflection?

Inspecting metadata during runtime.

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44. What is ADO.NET?

Low-level data access using:

• SqlConnection

• SqlCommand

• SqlDataReader

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45. What is Thread and Task in .NET?

Thread → independent execution path
Task → lightweight wrapper for async operations

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46. Explain SOLID Principles.

5 design principles for maintainable code:

• Single Responsibility

• Open Closed

• Liskov Substitution

• Interface Segregation

• Dependency Inversion

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47. What is Attribute in C#?

Metadata added to classes or methods.

Example:

[Authorize]
public class HomeController { }

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48. What is Filter in ASP.NET Core?

Executes logic before or after controller actions.
Types:

• Authorization

• Resource

• Action

• Exception

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49. What is Web API Versioning?

Manage multiple versions of APIs for backward compatibility.

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50. What is Health Check in ASP.NET Core?

Used to monitor the health of application and services in production.

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