.Net Interview Questions and Answers for 2 years experience

1. What is the difference between a class and a struct in C#?

   • Answer: Classes are reference types, meaning variables hold references to the objects. Structs are value types, meaning variables hold the actual data. Classes can have constructors, destructors, and inheritance; structs cannot. Classes are better suited for complex objects, while structs are preferable for small, simple data structures. Structs are typically allocated on the stack, while classes are allocated on the heap.

2. Explain the concept of garbage collection in .NET.

   • Answer: Garbage collection is an automatic memory management feature in .NET. It automatically reclaims memory occupied by objects that are no longer referenced by the application. This prevents memory leaks and simplifies memory management for developers. The garbage collector runs periodically, identifying and releasing unused memory. Different generations of garbage collection exist, optimizing the process for objects with varying lifespans.

3. What are delegates in C#? Give an example.

   • Answer: Delegates are type-safe function pointers. They allow you to pass methods as arguments to other methods. This enables features like event handling and callbacks. For example: `public delegate int MyDelegate(int x, int y);` defines a delegate that can point to any method that takes two integers as input and returns an integer.

4. What is LINQ and how does it work?

   • Answer: LINQ (Language Integrated Query) is a powerful feature that allows you to query data from various sources (databases, XML files, in-memory collections) using a consistent syntax. It integrates seamlessly with C# and uses a declarative style, specifying *what* data you want rather than *how* to retrieve it. LINQ translates your queries into optimized code for the underlying data source.

5. Explain the difference between IEnumerable and IQueryable.

   • Answer: Both are interfaces used for querying data, but `IEnumerable` executes queries in memory after the data has been retrieved, while `IQueryable` translates queries into expressions that can be executed remotely (e.g., in a database). `IQueryable` provides better performance for large datasets as it avoids transferring unnecessary data.

6. What is the purpose of an interface in C#?

   • Answer: An interface defines a contract that classes can implement. It specifies a set of methods, properties, and events that implementing classes *must* provide. Interfaces promote polymorphism and loose coupling, allowing different classes to interact without needing to know their specific implementation details.

7. What are generics in C# and why are they useful?

   • Answer: Generics allow you to write type-safe code that can work with different data types without losing type information. They avoid the need for boxing and unboxing, leading to performance improvements. Generics improve code reusability and reduce the risk of runtime type errors.

8. Describe the different types of exceptions in .NET.

   • Answer: .NET has a hierarchy of exception classes. Common types include `SystemException` (base class for many exceptions), `ArgumentException`, `IOException`, `NullReferenceException`, `OutOfMemoryException`, etc. Understanding exception types is crucial for robust error handling.

9. How do you handle exceptions in C#?

   • Answer: Use `try-catch-finally` blocks. The `try` block contains code that might throw an exception. The `catch` block handles specific exception types. The `finally` block contains code that always executes, regardless of whether an exception occurred (e.g., releasing resources).

10. What is ASP.NET MVC?

    • Answer: ASP.NET MVC (Model-View-Controller) is a web application framework that follows the MVC architectural pattern. It separates concerns into models (data and business logic), views (user interface), and controllers (handling user input and updating the model).

11. What is the difference between ViewBag, ViewData and TempData in ASP.NET MVC?

    • Answer: ViewBag is a dynamic object, allowing you to pass data to a view without defining strong types. ViewData is a dictionary object. TempData is used to pass data between controller actions (typically across redirects). ViewData and ViewBag are available only within the current request, whereas TempData persists across requests until accessed.

12. Explain the concept of Dependency Injection.

    • Answer: Dependency Injection is a design pattern where dependencies are provided to a class instead of the class creating them itself. This improves testability, maintainability, and loose coupling. It promotes better code organization and allows easier swapping of implementations.

13. What are different ways to implement Dependency Injection in .NET?

    • Answer: Constructor Injection, Property Injection, and Method Injection are common ways. Popular DI containers like Autofac, Ninject, and Unity simplify the process.

14. What is the purpose of the `using` statement in C#?

    • Answer: The `using` statement ensures that disposable objects (implementing `IDisposable`) are properly released even if exceptions occur. It's equivalent to wrapping the object in a `try-finally` block to call `Dispose()`.

15. What is asynchronous programming in C#? Explain the `async` and `await` keywords.

    • Answer: Asynchronous programming allows your code to continue executing other tasks while waiting for long-running operations (like network requests or I/O) to complete, improving responsiveness. `async` marks a method as asynchronous, and `await` pauses execution until an awaited task completes without blocking the thread.

16. What is Entity Framework Core?

    • Answer: Entity Framework Core (EF Core) is an object-relational mapper (ORM) that enables .NET developers to work with databases using objects instead of writing raw SQL queries. It simplifies database interactions and improves developer productivity.

17. Explain different database access methods in .NET.

    • Answer: ADO.NET (direct database access), Entity Framework Core (ORM), and other ORMs like NHibernate are common methods.

18. What is a Web API in ASP.NET?

    • Answer: ASP.NET Web API is a framework for building RESTful HTTP services that can be accessed from various clients (web browsers, mobile apps, etc.). It allows you to create APIs that expose your application's functionality.

19. What is the difference between GET and POST requests?

    • Answer: GET requests are used to retrieve data from a server, typically via a URL. POST requests are used to submit data to a server for processing (e.g., creating a new resource).

20. Explain RESTful principles.

    • Answer: REST (Representational State Transfer) is an architectural style for building web services. Key principles include using standard HTTP methods (GET, POST, PUT, DELETE), stateless communication, and resource-based URLs.

21. What are some common design patterns in .NET?

    • Answer: Singleton, Factory, Observer, Strategy, Decorator, and many more are widely used in .NET applications.

22. What is the role of a middleware component in ASP.NET Core?

    • Answer: Middleware components are modules in ASP.NET Core that perform actions on incoming requests and outgoing responses. They form a pipeline that processes each request before it reaches the controller and after the controller finishes processing.

23. Explain the concept of Inversion of Control (IoC).

    • Answer: IoC is a design principle where the control of object creation and dependency resolution is inverted. Instead of a class creating its dependencies, they are provided by an external container.

24. What is the difference between .NET Framework and .NET Core (now .NET)?

    • Answer: .NET Framework is a Windows-only framework, while .NET is cross-platform (Windows, macOS, Linux). .NET is more modular and has a more streamlined design. .NET Core (now .NET) is the successor to the .NET Framework.

25. What are some common tools used for .NET development?

    • Answer: Visual Studio, Visual Studio Code, ReSharper, .NET CLI, NuGet.

26. Explain the concept of SOLID principles.

    • Answer: SOLID is a set of design principles intended to make software designs more understandable, flexible, and maintainable: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.

27. How do you perform unit testing in .NET?

    • Answer: Use frameworks like NUnit, xUnit, or MSTest to write unit tests. Focus on testing individual units of code (classes, methods) in isolation.

28. What is code coverage and why is it important?

    • Answer: Code coverage measures the percentage of code that is executed during unit testing. High code coverage indicates better test completeness but doesn't guarantee correctness.

29. What is Reflection in .NET?

    • Answer: Reflection allows you to inspect and manipulate types, methods, properties, and other members of .NET assemblies at runtime. It's useful for dynamic code generation and other advanced scenarios.

30. Explain the concept of serialization and deserialization.

    • Answer: Serialization converts an object into a stream of bytes (or other format) for storage or transmission. Deserialization reconstructs the object from the stream.

31. What are some common serialization formats in .NET?

    • Answer: JSON, XML, Binary serialization.

32. How do you implement logging in a .NET application?

    • Answer: Use logging frameworks like NLog, log4net, or Serilog to record application events and errors to files or databases. This is crucial for debugging and monitoring.

33. What is a Razor view in ASP.NET MVC?

    • Answer: Razor views are templates that combine C# code with HTML to generate dynamic web pages. They use a concise syntax to embed C# expressions and statements within HTML.

34. What are partial views in ASP.NET MVC?

    • Answer: Partial views are reusable chunks of view code that can be included in other views. This improves code organization and reusability.

35. Explain the role of a controller in ASP.NET MVC.

    • Answer: Controllers handle user input, interact with models, and select the appropriate view to render.

36. What is Model Binding in ASP.NET MVC?

    • Answer: Model binding automatically populates controller action parameters with data from HTTP requests.

37. What is routing in ASP.NET MVC?

    • Answer: Routing maps incoming URLs to specific controller actions. This allows you to create clean and SEO-friendly URLs.

38. What is the difference between a view model and a domain model?

    • Answer: A domain model represents business entities, while a view model is a simplified version of the domain model tailored for specific views. View models may contain only the data needed by a view, enhancing separation of concerns.

39. How do you implement authentication and authorization in ASP.NET Core?

    • Answer: Use ASP.NET Core's built-in authentication and authorization features, which provide various options like cookie-based authentication, JWTs, and integration with OAuth 2.0 providers.

40. What is JWT (JSON Web Token)?

    • Answer: A JWT is a compact and self-contained way to transmit information securely between parties as a JSON object. It's often used for authentication.

41. Explain the concept of caching in .NET.

    • Answer: Caching stores frequently accessed data in memory for faster retrieval. This improves application performance.

42. What are some common caching mechanisms in .NET?

    • Answer: In-memory caching (using `MemoryCache`), distributed caching (like Redis or Memcached).

43. How do you manage application configuration in .NET?

    • Answer: Use configuration files (like `appsettings.json`), environment variables, or cloud-based configuration services.

44. What is the role of a repository pattern in .NET applications?

    • Answer: The repository pattern abstracts data access logic. It provides a clean interface for interacting with data sources, improving testability and maintainability.

45. What is a Unit of Work pattern?

    • Answer: The unit of work pattern manages transactions across multiple repositories or data access operations. It ensures that all changes are either committed or rolled back as a single unit.

46. How do you handle database transactions in .NET?

    • Answer: Use the `TransactionScope` class or database-specific transaction management mechanisms.

47. What are some common security best practices for .NET applications?

    • Answer: Input validation, output encoding, using parameterized queries to prevent SQL injection, proper authentication and authorization, regular security updates, and secure coding practices are essential.

48. What is cross-site scripting (XSS)? How do you prevent it?

    • Answer: XSS is a web security vulnerability where malicious scripts are injected into otherwise benign and trusted websites. Prevention includes input validation and output encoding (HTML encoding).

49. What is SQL injection? How do you prevent it?

    • Answer: SQL injection is a code injection technique used to attack data-driven applications, in which malicious SQL statements are inserted into an entry field for execution (e.g., to dump a database). Prevention relies on parameterized queries or stored procedures.

50. Explain the difference between synchronous and asynchronous programming.

    • Answer: Synchronous programming executes tasks sequentially; one task must complete before the next begins. Asynchronous programming allows multiple tasks to run concurrently, improving responsiveness.

51. What is the purpose of the `async` and `await` keywords in C#?

    • Answer: `async` designates an asynchronous method that can use `await`. `await` suspends execution of an asynchronous method until a task completes without blocking the current thread.

52. What is a task in .NET?

    • Answer: A task represents an asynchronous operation. It provides methods for managing and monitoring the operation's progress and result.

53. How do you handle cancellation of asynchronous operations?

    • Answer: Use the `CancellationToken` class to signal cancellation requests to asynchronous operations.

54. Explain the concept of thread pooling in .NET.

    • Answer: Thread pooling reuses a set of worker threads to execute tasks, reducing the overhead of creating and destroying threads for each task. This improves performance and resource management.

55. What is the difference between `Thread` and `Task` in .NET?

    • Answer: `Thread` represents a system-level thread, while `Task` represents an asynchronous operation that might run on a thread pool thread. `Task` is generally preferred for asynchronous operations.

56. What is the purpose of the `lock` keyword in C#?

    • Answer: The `lock` keyword ensures that only one thread can access a critical section of code at a time, preventing race conditions and data corruption in multithreaded applications.

57. What are some common ways to improve the performance of a .NET application?

    • Answer: Efficient algorithm selection, caching, database optimization, asynchronous programming, using profiling tools to identify bottlenecks, and code optimization.

58. How do you profile a .NET application?

    • Answer: Use profiling tools like dotTrace, ANTS Performance Profiler, or Visual Studio's built-in profiling features to analyze application performance and identify bottlenecks.

59. What is continuous integration and continuous deployment (CI/CD)?

    • Answer: CI/CD is a set of practices that automate the process of building, testing, and deploying software. It improves software quality and reduces deployment time.

60. What are some common CI/CD tools used with .NET?

    • Answer: Azure DevOps, Jenkins, GitHub Actions, GitLab CI.

61. How do you deploy a .NET application to Azure?

    • Answer: Use Azure DevOps, Azure CLI, or Visual Studio's publish features to deploy your application to Azure App Service, Azure Kubernetes Service (AKS), or other Azure services.

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