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.

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.

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.

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.

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.

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.

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.

8. What is OOPS in C#?

Answer:
OOPS stands for:

Encapsulation
Abstraction
Inheritance
Polymorphism

It helps create modular, maintainable, and reusable code.

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.

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().

11. What is Polymorphism?

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

Example:


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

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

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

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

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.

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>();

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

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

19. What is Code-First approach?

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

20. What is Database-First approach?

Database already exists → EF generates models and DbContext.

21. What is Migration in EF Core?

Answer:
Migrations track database schema changes.

Commands:


Add-Migration Init
Update-Database

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);

23. What is async and await?

Answer:
Used for asynchronous programming to avoid thread blocking.

Example:


await Task.Delay(1000);

24. What is Garbage Collection in .NET?

Answer:
Automatic memory management that frees unused objects.

Generations:

Gen 0
Gen 1
Gen 2

25. What is IDisposable Interface?

Used to release unmanaged resources manually.

Example:


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

26. What is a Constructor and Destructor?

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

27. What is Singleton Pattern?

Ensures only one instance of a class exists.

Example:


public static readonly Singleton Instance = new Singleton();

28. What is Routing in ASP.NET Core?

Matches incoming HTTP requests to endpoints.

Example:


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

29. What is Model Binding?

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

30. What is ViewModel?

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

31. What is REST API?

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

32. Difference between GET and POST.

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

33. What is JWT Token?

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

Header
Payload
Signature

34. What is Swagger?

API documentation and testing tool built on OpenAPI specification.

35. What is Microservices Architecture?

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

36. What is Kestrel?

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

37. What is Configuration in ASP.NET Core?

Manages app settings using:

appsettings.json
Environment variables
Azure Key Vault

38. What is CORS?

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

39. What is a NuGet Package?

Dependency manager for .NET libraries.

40. What is .NET Standard?

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

41. Explain Sealed Class.

Cannot be inherited, used for security/performance.

42. What is a Partial Class?

A class split into multiple files.

43. What is Reflection?

Inspecting metadata during runtime.

44. What is ADO.NET?

Low-level data access using:

SqlConnection
SqlCommand
SqlDataReader

45. What is Thread and Task in .NET?

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

46. Explain SOLID Principles.

5 design principles for maintainable code:

Single Responsibility
Open Closed
Liskov Substitution
Interface Segregation
Dependency Inversion

47. What is Attribute in C#?

Metadata added to classes or methods.

Example:


[Authorize]
public class HomeController { }

48. What is Filter in ASP.NET Core?

Executes logic before or after controller actions.
Types:

Authorization
Resource
Action
Exception

49. What is Web API Versioning?

Manage multiple versions of APIs for backward compatibility.

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

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

Sunday, November 23, 2025

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

1. What is .NET Framework?

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

3. What is the CLR?

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

5. What is C#?

6. What is MSIL/IL Code?

7. What is JIT Compiler?

8. What is OOPS in C#?

9. Explain Encapsulation with example.

10. What is Inheritance in C#?

11. What is Polymorphism?

12. Difference between Abstract Class and Interface.

13. What are Value Types and Reference Types?

14. What is Boxing and Unboxing?

15. What is ASP.NET Core?

16. What are Middleware components?

17. What is Dependency Injection (DI)?

18. What is Entity Framework Core?

19. What is Code-First approach?

20. What is Database-First approach?

21. What is Migration in EF Core?

22. What is LINQ?

23. What is async and await?

24. What is Garbage Collection in .NET?

25. What is IDisposable Interface?

26. What is a Constructor and Destructor?

27. What is Singleton Pattern?

28. What is Routing in ASP.NET Core?

29. What is Model Binding?

30. What is ViewModel?

31. What is REST API?

32. Difference between GET and POST.

33. What is JWT Token?

34. What is Swagger?

35. What is Microservices Architecture?

36. What is Kestrel?

37. What is Configuration in ASP.NET Core?

38. What is CORS?

39. What is a NuGet Package?

40. What is .NET Standard?

41. Explain Sealed Class.

42. What is a Partial Class?

43. What is Reflection?

44. What is ADO.NET?

45. What is Thread and Task in .NET?

46. Explain SOLID Principles.

47. What is Attribute in C#?

48. What is Filter in ASP.NET Core?

49. What is Web API Versioning?

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

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