ASP.NET Interview Questions and Answers for freshers

1. What is ASP.NET?

   • Answer: ASP.NET is a server-side web application framework developed by Microsoft. It allows developers to build dynamic web pages, web applications, and web services using .NET languages like C# and VB.NET.

2. Explain the difference between ASP.NET Web Forms and ASP.NET MVC.

   • Answer: ASP.NET Web Forms uses a server-side event-driven model, employing controls and postbacks. ASP.NET MVC (Model-View-Controller) follows a separation of concerns pattern, improving testability and maintainability.

3. What is a ViewState in ASP.NET Web Forms?

   • Answer: ViewState is a mechanism that preserves the state of server controls between postbacks. It stores control values in a hidden field on the page.

4. What are the advantages of using Master Pages in ASP.NET?

   • Answer: Master Pages promote code reusability by providing a consistent layout and design across multiple pages. Changes made to the Master Page automatically update all child pages.

5. What is the role of Global.asax in an ASP.NET application?

   • Answer: Global.asax is the application file that contains code for handling application-level events like Application_Start, Session_Start, Application_End, and Session_End.

6. Explain the concept of Routing in ASP.NET MVC.

   • Answer: Routing maps incoming URLs to specific controller actions. It allows for creating SEO-friendly URLs and decoupling URLs from file system structure.

7. What are Model, View, and Controller in ASP.NET MVC?

   • Answer: Model represents the data, View is responsible for displaying data to the user, and Controller manages user interaction, processes data, and selects the appropriate View.

8. What is a Partial View in ASP.NET MVC?

   • Answer: A Partial View is a small, reusable view that can be rendered within a larger view. It helps in separating concerns and improving code maintainability.

9. How do you handle exceptions in ASP.NET?

   • Answer: Exceptions can be handled using try-catch blocks and custom error pages. The global.asax file can also be used to handle unhandled exceptions.

10. What are different types of HTTP verbs?

    • Answer: GET, POST, PUT, DELETE, PATCH are common HTTP verbs used for different types of requests. GET retrieves data, POST submits data, PUT updates data, DELETE removes data, and PATCH partially updates data.

11. Explain the concept of Session Management in ASP.NET.

    • Answer: Session Management allows storing user-specific data during a user's interaction with a web application. It utilizes server-side storage to maintain state across multiple requests from the same user.

12. What are cookies and how are they used in ASP.NET?

    • Answer: Cookies are small pieces of data stored on the client-side browser. ASP.NET uses cookies to store user preferences, session IDs, and other data that needs to be persisted across multiple requests.

13. What is the difference between InProc, StateServer, and SQL Server session modes?

    • Answer: InProc stores session data in the web application's memory; StateServer stores it in a separate Windows service; SQL Server stores it in a SQL Server database. InProc is fastest but not scalable, while the others offer better scalability and availability.

14. What is AJAX and how is it used in ASP.NET?

    • Answer: AJAX (Asynchronous JavaScript and XML) allows updating parts of a web page without reloading the entire page. In ASP.NET, AJAX is often used with UpdatePanels or by directly using JavaScript libraries like jQuery to make asynchronous requests to the server.

15. Explain the use of Web API in ASP.NET.

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

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

    • Answer: The `using` statement ensures that resources (like files or database connections) are properly closed even if exceptions occur. It implements the IDisposable pattern.

17. What is LINQ (Language Integrated Query)?

    • Answer: LINQ provides a consistent way to query and manipulate data from various sources (databases, XML, collections) using C# code.

18. Explain the difference between GET and POST requests.

    • Answer: GET requests are used to retrieve data from the server and are typically idempotent (performing the same action multiple times has the same effect). POST requests are used to submit data to the server to be processed (e.g., creating a new resource).

19. What is the role of a Controller in ASP.NET MVC?

    • Answer: The Controller handles user requests, interacts with the Model to retrieve or manipulate data, and selects the appropriate View to display the results.

20. What are the different types of authentication in ASP.NET?

    • Answer: ASP.NET supports various authentication methods including Forms Authentication, Windows Authentication, and OAuth. Forms Authentication uses a login form, Windows Authentication uses the Windows user credentials, and OAuth relies on third-party authentication providers.

21. How do you implement authorization in ASP.NET?

    • Answer: Authorization controls access to resources based on the user's identity. It can be implemented using roles, attributes (like [Authorize]), and custom authorization modules.

22. 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. This improves testability, modularity, and maintainability.

23. What is a Razor View Engine?

    • Answer: The Razor View Engine is a templating engine used in ASP.NET MVC and Web Pages. It uses a concise syntax to embed server-side code within HTML.

24. What is the difference between Server-side and Client-side validation?

    • Answer: Server-side validation occurs on the server after the form is submitted, providing robust security. Client-side validation occurs in the browser before submission, providing immediate feedback to the user but is less secure.

25. What is the purpose of a Web.config file?

    • Answer: Web.config stores application-specific settings, including connection strings, configuration settings, and security settings.

26. What is caching in ASP.NET?

    • Answer: Caching stores frequently accessed data in memory to improve performance. ASP.NET offers various caching mechanisms, including Output Caching, Data Caching, and Fragment Caching.

27. Explain the difference between `@model` and `@Html.DisplayFor` in Razor.

    • Answer: `@model` specifies the model type for the view. `@Html.DisplayFor` is a helper method that displays properties of the model based on their type.

28. What are some common HTTP status codes?

    • Answer: 200 (OK), 404 (Not Found), 500 (Internal Server Error), 301 (Moved Permanently), 400 (Bad Request).

29. What is the difference between a ViewBag and a ViewData?

    • Answer: ViewBag is a dynamic property bag introduced in ASP.NET MVC 3, offering type safety. ViewData is a dictionary-like object available in earlier versions.

30. How do you handle file uploads in ASP.NET?

    • Answer: File uploads are handled using the `FileUpload` control (Web Forms) or by processing the request in the Controller (MVC). Security considerations, such as checking file types and sizes, are crucial.

31. Explain the concept of Bundling and Minification.

    • Answer: Bundling combines multiple JavaScript and CSS files into a smaller number of files to reduce HTTP requests. Minification removes unnecessary characters from code to reduce file sizes.

32. What is SignalR?

    • Answer: SignalR is a library that simplifies building real-time web applications. It enables bi-directional communication between server and client.

33. What are some common design patterns used in ASP.NET?

    • Answer: MVC, Dependency Injection, Repository, Factory, Singleton are some common design patterns used in ASP.NET applications.

34. How can you improve the performance of an ASP.NET application?

    • Answer: Techniques include caching, database optimization, code optimization, using content delivery networks (CDNs), and asynchronous programming.

35. What are some security best practices for ASP.NET applications?

    • Answer: Input validation, output encoding, using parameterized queries, secure authentication and authorization, regular security updates, and using HTTPS are crucial.

36. What is the difference between a Web Garden and App Pool?

    • Answer: A Web Garden allows multiple worker processes to handle requests for a single application, improving scalability. An App Pool is a logical grouping of websites or applications, providing isolation and resource management.

37. Explain the concept of a custom HTTP handler.

    • Answer: A custom HTTP handler allows intercepting requests based on the URL and handling them differently. It provides extensibility to the ASP.NET pipeline.

38. Explain the concept of a custom HTTP module.

    • Answer: A custom HTTP module allows intercepting events throughout the HTTP request pipeline. It can be used for logging, authentication, and other cross-cutting concerns.

39. What is the role of the `web.config` transform feature?

    • Answer: Web.config transforms allow modifying the `web.config` file based on the build configuration (e.g., Debug, Release). This simplifies deploying to different environments.

40. What is the difference between `Redirect` and `Transfer` in ASP.NET?

    • Answer: `Redirect` sends an HTTP redirect to the browser, resulting in a new request. `Transfer` transfers execution to another page on the server without a new request, which is faster but can cause problems with the URL.

41. What are the benefits of using a Content Delivery Network (CDN)?

    • Answer: CDNs improve performance by caching static content (images, CSS, JavaScript) on servers closer to users, reducing latency and improving website loading times.

42. What is Entity Framework (EF)?

    • Answer: EF is an ORM (Object-Relational Mapper) that allows developers to interact with databases using objects instead of writing SQL queries directly.

43. What are some common issues you might encounter while developing ASP.NET applications?

    • Answer: Common issues include debugging problems, handling exceptions, database connection issues, performance bottlenecks, security vulnerabilities, and deployment challenges.

44. How do you debug ASP.NET applications?

    • Answer: ASP.NET applications are debugged using Visual Studio's debugging tools, which allow setting breakpoints, stepping through code, inspecting variables, and using the immediate window.

45. What is the role of the `web.config` file in deployment?

    • Answer: The `web.config` file contains settings specific to the deployment environment (database connection strings, configuration settings). It needs to be appropriately configured for the target environment.

46. Explain the concept of asynchronous programming in ASP.NET.

    • Answer: Asynchronous programming allows handling long-running operations without blocking the main thread, improving responsiveness and scalability. It's particularly useful for I/O-bound operations.

47. What are some tools used for testing ASP.NET applications?

    • Answer: Tools like NUnit, MSTest, and xUnit are used for unit testing. Integration testing and UI testing can be done with Selenium or other automated testing frameworks.

48. What is the difference between a static and an instance method?

    • Answer: A static method belongs to the class itself and is called using the class name. An instance method belongs to an object (instance) of the class and is called using an object reference.

49. Explain the concept of inheritance in C#.

    • Answer: Inheritance is a mechanism where a class (derived class) inherits properties and methods from another class (base class). It promotes code reusability and establishes an "is-a" relationship.

50. What is polymorphism?

    • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. It enables flexibility and extensibility.

51. What is encapsulation?

    • Answer: Encapsulation bundles data and methods that operate on that data within a class, hiding internal details and protecting data integrity.

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

    • Answer: An interface defines a contract that classes must implement. It specifies methods, properties, and events without providing their implementation.

53. What is abstract class?

    • Answer: An abstract class cannot be instantiated directly but serves as a base class for other classes. It can contain both abstract methods (without implementation) and concrete methods.

54. What is a constructor?

    • Answer: A constructor is a special method in a class that is automatically called when an object of the class is created. It is used to initialize the object's properties.

55. What is a destructor?

    • Answer: A destructor is a special method in a class that is automatically called when an object of the class is garbage collected. It is used to release resources held by the object.

56. What is the difference between `ref` and `out` parameters?

    • Answer: Both `ref` and `out` parameters pass variables by reference. `ref` requires the variable to be initialized before being passed, while `out` does not.

57. What is a delegate in C#?

    • Answer: A delegate is a type that represents a reference to a method. It is used for event handling and callback mechanisms.

58. What is an event in C#?

    • Answer: An event is a notification mechanism that allows one object to notify other objects when something significant happens. It uses delegates to handle event subscriptions and invocations.

59. What is a generic class in C#?

    • Answer: A generic class allows creating classes and methods that can work with various data types without needing to write separate code for each type.

60. What is exception handling in C#?

    • Answer: Exception handling uses `try-catch` blocks to gracefully handle runtime errors, preventing application crashes. It allows handling different types of exceptions separately.

61. What is the difference between `==` and `Equals()`?

    • Answer: `==` compares references for reference types and values for value types. `Equals()` is a method that can be overridden to provide custom comparison logic for objects.

62. What is the `null` coalescing operator (`??`) in C#?

    • Answer: The null coalescing operator returns the left-hand operand if it's not null; otherwise, it returns the right-hand operand.

63. What is the null-conditional operator (`?.`) in C#?

    • Answer: The null-conditional operator safely accesses members of an object only if the object is not null, preventing `NullReferenceException` errors.

64. Explain LINQ methods `Where`, `Select`, and `OrderBy`.

    • Answer: `Where` filters elements based on a condition. `Select` projects elements into a new form. `OrderBy` sorts elements in ascending order.

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