Are you preparing for a .NET Developer interview? Here's a quick and clear guide covering OOPs, .NET, MVC, Web API, and SQL Server questions with short, simple answers — perfect for quick revision!
🔹 OOPs (Object-Oriented Programming)
1. What are the 4 pillars of OOP?
- Encapsulation – Bundling data and methods together
- Abstraction – Hiding complexity, showing only essentials
- Inheritance – Reusing code via base/derived classes
- Polymorphism – One interface, many implementations (overloading/overriding)
2. Difference between Abstraction and Encapsulation
| Concept | Abstraction | Encapsulation |
|---|---|---|
| Focus | Hides what happens inside | Hides how data is stored |
| Use | Interfaces/abstract classes | Access modifiers |
3. Interface vs Abstract Class in C#
| Feature | Abstract Class | Interface |
|---|---|---|
| Methods | Can have definitions | Only signatures (till C# 8) |
| Modifiers | Access modifiers allowed | All members are public |
| Inheritance | Single inheritance | Multiple interfaces supported |
4. Overloading vs Overriding
- Overloading: Same method name, different parameters (compile-time)
- Overriding: Redefines base method in derived class (runtime)
🔹 .NET & C# Interview Questions
5. Difference between ref and out?
- ref: Must be initialized before passing
- out: No need to initialize; must be assigned inside the method
6. What is Garbage Collection in .NET?
The Garbage Collector (GC) automatically frees memory by destroying unused objects.
7. Difference between == and .Equals()
- ==: Compares values (for value types) or references (for objects)
- .Equals(): Can compare content, can be overridden
🔹 ASP.NET MVC Questions
8. What is MVC Architecture?
- Model: Business logic & data
- View: UI layer
- Controller: Handles user input & updates Model/View
9. What is Routing in MVC?
Maps URLs to controller/action methods.
routes.MapRoute("Default", "{controller}/{action}/{id}");
🔹 10. TempData vs ViewData vs ViewBag
| Feature | ViewData | ViewBag | TempData |
|---|---|---|---|
| Type | Dictionary | Dynamic | Dictionary |
| Lifetime | Current request | Current request | Current + next request |
| Use Case | Data to View | Data to View | Across redirects |
🔹 11. What are Action Filters in MVC?
Action Filters allow you to run logic before or after an action method executes in a controller.
Examples:
-
[Authorize]– Restrict access -
[HandleError]– Handle exceptions -
[OutputCache]– Cache output
🔹 Web API Questions
12. What is Web API in .NET?
ASP.NET Web API is a framework to build RESTful HTTP services, used in web, mobile, or desktop applications. It supports content negotiation (JSON/XML) and is lightweight.
13. Difference: Web API vs MVC
| Feature | MVC | Web API |
|---|---|---|
| Purpose | Returns HTML Views | Returns data (JSON, XML) |
| Return Type | ViewResult |
JsonResult, IHttpActionResult
|
14. How to Secure Web API?
- 🔐 Use JWT tokens or OAuth 2.0
- 🛡️ Implement Authorization filters
- 🔒 Use HTTPS to encrypt communication
15. Common HTTP Verbs in Web API
- GET – Read data
- POST – Create new data
- PUT – Replace entire resource
- PATCH – Update partial resource
- DELETE – Remove data
🔹 SQL Server Interview Questions
16. WHERE vs HAVING
-
WHERE: Filters rows before
GROUP BY -
HAVING: Filters groups after
GROUP BY
17. Types of SQL Joins
- 🔹 INNER JOIN – Returns matching rows from both tables
- 🔹 LEFT JOIN – All rows from left + matched rows from right
- 🔹 RIGHT JOIN – All rows from right + matched from left
- 🔹 FULL OUTER JOIN – All rows when there's a match in either table
- 🔹 CROSS JOIN – Cartesian product (every combination)
18. DELETE vs TRUNCATE
| Feature | DELETE | TRUNCATE |
|---|---|---|
| Logging | Logs each row | Minimal logging |
| WHERE | Allowed | Not allowed |
| Rollback | Yes | Not guaranteed |
19. What is a Stored Procedure?
A Stored Procedure is a precompiled set of SQL statements stored in the database to perform a specific task.
CREATE PROCEDURE GetEmployees
AS
BEGIN
SELECT * FROM Employees
END
🔹 20. What is Indexing in SQL?
Indexing is a technique used to speed up data retrieval in SQL tables by reducing the amount of data the database engine has to scan.
🔍 Types of Indexes:
- 🔸 Clustered Index – Sorts and stores data rows in the table based on the key values. Only one per table.
- 🔸 Non-Clustered Index – Stores index separately from actual table data. Multiple allowed per table.
- 🔸 Unique Index – Ensures all values in the index key are unique.
- 🔸 Full-Text Index – Used for searching text-based columns (e.g., LIKE, CONTAINS).
💡 Quick Tip:
🎯 Be clear and confident in your explanations.
🛠️ Practice real-world SQL queries and indexing scenarios.
📚 Revise these questions regularly to stay sharp before interviews.
📌 Pro Tip:
When dealing with large datasets, indexing can drastically improve performance — especially on WHERE, JOIN, and ORDER BY queries.
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