Mastering the .NET Interview | Top .NET Interview Questions and Answers

1. Tpoint Tech Mastering the .NET Interview This guide is designed to equip you with the essential knowledge and strategies needed to excel in .NET interviews, whether you're targeting roles in C#, ASP.NET Core, or Azure. We'll cover core concepts, practical applications, and how to effectively navigate common technical and behavioral questions, setting you up for success in your job search. https://www.tpointtech.com/dot-net-interview-questions +91-9599086977 .NET Tutorial

2. Foundational C# & Object-Oriented Programming (OOP) Explain `async` and `await`. `async` marks a method as awaitable, allowing it to pause execution without blocking the calling thread. `await` pauses the `async` method until the awaited `Task` completes. This is vital for maintaining UI responsiveness in desktop applications and ensuring scalability in web APIs by freeing up threads for other requests. Describe SOLID principles. SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) are a set of design principles aimed at making software designs more understandable, flexible, and maintainable. Applying SOLID can significantly reduce coupling between components and studies show it can lead to 20% faster bug resolution due to clearer code structures. Differentiate `abstract` classes and `interfaces`. An `abstract` class can have concrete and abstract methods, and can contain fields, properties, and constructors. A class can only inherit from one `abstract` class. An `interface`, however, defines a contract that implementing classes must adhere to, containing only method signatures, properties, and events (though .NET Core 8 introduced default interface methods). A class can implement multiple interfaces, making them suitable for defining capabilities. .NET Tutorial

3. ASP.NET Core & Web Development What is Middleware in ASP.NET Core? Explain Dependency Injection (DI) in ASP.NET Core. Middleware components form a pipeline that handles HTTP requests and responses. Each component can perform operations before and after the next component in the pipeline. Examples include authentication, routing, and error handling middleware. This modular approach allows for a highly customizable and efficient request processing flow, leading to up to 30% faster processing than traditional web pipelines. Dependency Injection is a design pattern used to achieve Inversion of Control (IoC) between classes and their dependencies. ASP.NET Core has a built-in IoC container that manages the instantiation and lifetime of services (singleton, scoped, transient). This pattern improves the testability, maintainability, and scalability of applications by decoupling components. Benefits of ASP.NET Core over ASP.NET Framework? ASP.NET Core offers significant advantages: it's cross-platform (runs on Windows, Linux, macOS), boasts superior performance (up to 8x faster than Node.js in some benchmarks), is modular with NuGet packages, and is open-source. These features make it highly adaptable for modern cloud-based and containerized applications, offering greater flexibility and efficiency for developers.

4. Data Access & ORM with Entity Framework Core (EF Core) How does EF Core's change tracking work? EF Core tracks changes to entities loaded from the database by default. It does this by maintaining snapshots of original values or by using proxies. When `SaveChanges()` is called, EF Core compares the current state of entities with their original state to determine which properties have changed, then generates and executes optimized update statements, reducing network traffic by up to 60%. Discuss `DbSet` vs. `IQueryable`. `DbSet` represents a collection of entities in the `DbContext` and corresponds to a table in the database. It allows basic CRUD operations. `IQueryable` is an interface that enables deferred execution, meaning queries are built up in memory and executed only when the results are materialized (e.g., when you call `ToList()`). This allows for highly optimized SQL generation by the ORM. Explain Migrations in EF Core. EF Core Migrations provide a way to evolve your database schema as your model changes. You create migration files (e.g., using `Add-Migration`) that contain code to apply (Up) and revert (Down) schema changes. The `Update-Database` command then applies these migrations to your database, automating schema updates and ensuring consistency across development, testing, and production environments. .NET Tutorial

5. Architecture & Design Patterns When would you use Microservices vs. Monolith? 1 Choose a monolith for smaller, less complex applications due to its simplicity and easier deployment. Microservices are better for large, complex systems requiring high scalability, independent deployments, and technology diversity. While microservices can reduce time-to-market by 20-30% for large systems, they introduce increased operational complexity, distributed debugging challenges, and higher infrastructure costs. Describe the Model-View-Controller (MVC) pattern. 2 MVC is a popular architectural pattern that separates an application into three main components: Model (data and business logic), View (user interface), and Controller (handles user input and updates the Model and View). This separation of concerns improves modularity, testability, and maintainability, making it a widely adopted pattern in ASP.NET Core for web applications. What is CQRS (Command Query Responsibility Segregation)? 3 CQRS separates the concerns of reading data (queries) from writing data (commands). This means you have separate models and often separate data stores for read and write operations. The benefit is optimized performance: write operations can be simple and transactional, while read operations can be highly optimized for querying, enabling independent scaling of reads up to 10x for read-heavy applications and improving overall system responsiveness.

6. Advanced Topics & Performance Optimization How do you handle concurrency in .NET? Concurrency is managed using mechanisms like `lock` (for mutual exclusion), `Monitor` (more flexible locking), `ReaderWriterLockSlim` (for read-heavy scenarios), and thread-safe `Concurrent Collections`. `Interlocked` operations provide atomic operations for simple variables. These tools prevent race conditions and deadlocks, which are crucial for ensuring data integrity and high performance in multi-threaded applications. Explain garbage collection (GC) in .NET. .NET's GC is an automatic memory management system that reclaims memory occupied by objects no longer in use. It is generational, meaning it divides the heap into generations (Gen 0, Gen 1, Gen 2) based on object lifespan. Most new objects are short-lived (95% are Gen 0 collections, which are very fast), optimizing performance by focusing collection efforts on areas most likely to contain garbage. Optimize a .NET application's performance. Performance optimization involves several strategies: using profiling tools (Visual Studio Profiler, dotTrace) to identify bottlenecks; leveraging `async`/`await` for non-blocking I/O; implementing caching (in-memory, distributed); optimizing database queries; minimizing object allocations to reduce GC pressure; and utilizing `Span` for efficient memory manipulation, especially in high-performance scenarios. .NET Tutorial

7. Behavioral Questions & Best Practices 1 2 3 Describe a challenging technical problem you solved. How do you stay updated with .NET technologies? What are your strengths/weaknesses as a developer? Use the STAR method (Situation, Task, Action, Result) to structure your answer. Detail the problem's context, your role, the steps you took to solve it (including any obstacles and how you overcame them), and the positive outcome. Emphasize your problem-solving process and any lessons learned. Showcase your commitment to continuous learning. Mention specific sources like official Microsoft documentation, active participation in community forums (e.g., Stack Overflow), following influential blogs, attending conferences (like Build or .NET Conf), and engaging with open-source projects. Over 200,000 active .NET developers globally contribute to the ecosystem, making community engagement invaluable. Demonstrate self-awareness and a growth mindset. For strengths, provide specific examples (e.g., strong debugging skills, collaborative teamwork, efficient problem-solving). For weaknesses, mention an area you're actively working to improve and outline concrete steps you're taking to address it. Frame weaknesses as opportunities for growth. .NET Tutorial

8. Tpoint Tech Conclusion: Beyond the Answers Beyond just knowing the answers, demonstrating a deeper understanding and passion for software development will set you apart. 1 2 3 Deep Understanding Problem-Solving Continuous Learning Explain *why* concepts are important, not just *what* they are. Show your grasp of the underlying principles and trade-offs. Showcase your critical thinking by walking through your thought process for complex scenarios and hypothetical challenges. Demonstrate your passion for technology by discussing personal projects, contributions to the community, and explorations of new tech. Action Item: Dedicate time to practicing coding exercises on platforms like LeetCode or HackerRank, focusing on problems that can be solved with .NET. This reinforces your practical skills and helps solidify your understanding of algorithms and data structures. .NET Tutorial