Top .NET Interview Questions for 2024-2025

This article compiles the most frequently asked technical interview questions for .NET developers during 2024 and 2025. These questions are based on real-world experiences and trusted sources to help you better prepare for your upcoming technical interviews.

🧠 .NET Basics and Architecture

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

• .NET Framework is designed for Windows applications, whereas .NET Core is a cross-platform, open-source version suitable for Windows, Linux, and macOS. From .NET 5 onwards, both are unified into a single platform known as .NET.

2. What is CLR and what are its responsibilities?

• CLR (Common Language Runtime) is the execution environment for .NET applications, responsible for memory management, garbage collection, exception handling, and type safety.

3. What are Assemblies in .NET?

• Assemblies are executable (.exe) or library (.dll) files that contain compiled code and metadata required for .NET applications. They play a crucial role in versioning, security, and deployment.

💡 Advanced C# and OOP Concepts

4. What is the difference between a Class and an Interface?

• Classes can have implementation, fields, and properties, while Interfaces only define method signatures and properties without implementation.

5. What is the difference between an Abstract Class and an Interface?

• Abstract classes can have both defined and undefined methods, whereas Interfaces only contain method signatures.

6. What is the difference between ref and out parameters?

• ref parameters must be initialized before being passed, while out parameters do not require initialization and are used for returning values from methods.

7. What is LINQ and what are its benefits?

• LINQ (Language Integrated Query) allows developers to write queries directly in C# for collections, databases, and XML, making code more readable and maintainable.

🧩 Advanced Concepts and Optimization

8. What is the difference between IEnumerable and IQueryable?

• IEnumerable is suitable for in-memory collections and executes queries in memory, while IQueryable is designed for database operations and executes queries at the database level.

9. What is Dependency Injection and its benefits?

• Dependency Injection (DI) is a design pattern that injects dependencies into classes, improving testability and maintainability. ASP.NET Core has built-in support for DI.

10. What is the difference between Task and Thread?

• Thread is a basic unit of execution, while Task is a higher-level abstraction for asynchronous programming that manages resources more efficiently.

11. What is the role of async and await in C#?

• These keywords simplify asynchronous programming, allowing long-running operations without blocking the main thread.

🛠️ ASP.NET Core and Web API

12. How does the MVC pattern work in ASP.NET?

• MVC (Model-View-Controller) divides an application into three interconnected components to separate business logic from UI.

13. How do you implement a RESTful API in .NET?

• Using ASP.NET Core Web API, developers define controllers with specific routes, create data models, and leverage Dependency Injection for service management.

14. How do you secure a Web API?

• Using JWT for authentication, enabling HTTPS, and applying authorization policies and filters in ASP.NET Core.

🗃️ Database and Entity Framework

15. What is Entity Framework and its advantages?

• Entity Framework (EF) is an ORM (Object-Relational Mapper) that allows developers to interact with databases using .NET objects instead of SQL queries.

16. What is the difference between Lazy Loading and Eager Loading?

• Lazy Loading loads data only when it is accessed, while Eager Loading fetches all related data along with the main entity.

17. What is the difference between Clustered and Non-Clustered Indexes in SQL Server?

• A Clustered Index sorts and stores data rows in the table, while a Non-Clustered Index maintains a separate structure pointing to the actual data.

🧰 Tools and Best Practices

18. What is NuGet and its purpose?

• NuGet is a package manager for .NET that allows developers to add libraries and dependencies to their projects easily.

19. How do you optimize the performance of a .NET application?

• By caching data, reducing database queries, using asynchronous programming, and managing resources efficiently.

20. What are common design patterns in .NET?

• Patterns like Singleton, Repository, and Factory are used for resource management, data abstraction, and object creation without exposing the instantiation logic.