Dotnet framework interview questions and answers

 

1. What is the .NET Framework?

• The .NET Framework is a software development platform developed by Microsoft.
• It provides a consistent programming model and a comprehensive set of libraries to build various applications such as web, desktop, and mobile apps.
• It consists of two major components:
  • Common Language Runtime (CLR): Handles memory management, exception handling, and garbage collection.
  • .NET Framework Class Library (FCL): Provides reusable classes and APIs for development.

Example:

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello, .NET Framework!");
    }
}

2. What is the Common Language Runtime (CLR)?

• CLR is the heart of the .NET Framework, responsible for executing .NET programs.
• It provides key services:
  • Memory management (using garbage collection).
  • Exception handling.
  • Thread management.
  • Security management.

Key Features of CLR:

• Just-In-Time (JIT) Compilation: Converts Intermediate Language (IL) code to machine code.
• Garbage Collection (GC): Automatically frees memory by removing objects that are no longer in use.

Example:

public class Example
{
    public void ShowMessage()
    {
        Console.WriteLine("CLR manages this execution.");
    }
}

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

• .NET Framework:
  • Runs only on Windows.
  • Used for building Windows-specific applications like desktop apps.
  • Larger runtime and library support.
• .NET Core:
  • Cross-platform (supports Windows, Linux, macOS).
  • Lightweight and modular.
  • Primarily used for web, cloud, and cross-platform apps.

4. What are Assemblies in .NET?

• Assemblies are the building blocks of a .NET application.
• An assembly is a compiled code that CLR can execute. It can be either an EXE (for applications) or a DLL (for reusable components).

Types of Assemblies:

• Private Assembly: Used by a single application.
• Shared Assembly: Can be shared across multiple applications (e.g., libraries stored in GAC).

Example:

// Compiling this code will create an assembly (DLL or EXE)
public class SampleAssembly
{
    public void DisplayMessage()
    {
        Console.WriteLine("This is an assembly example.");
    }
}

5. What is the Global Assembly Cache (GAC)?

• GAC is a machine-wide code cache that stores assemblies specifically designated to be shared by several applications on the computer.
• Assemblies in GAC are strongly named and allow multiple versions of the same assembly to be maintained side by side.

Example:

// To add an assembly to the GAC (in command prompt)
gacutil -i MyAssembly.dll

6. What are Namespaces in .NET?

• Namespaces are used to organize classes and other types in .NET.
• They prevent naming conflicts by logically grouping related classes.

Example:

namespace MyNamespace
{
    public class MyClass
    {
        public void Greet()
        {
            Console.WriteLine("Hello from MyNamespace!");
        }
    }
}

7. What is Managed Code?

• Managed Code is the code that runs under the control of the CLR.
• CLR manages execution, garbage collection, and other system services for the code.

Example:

// This is managed code because it's executed by CLR
public class ManagedCodeExample
{
    public void Print()
    {
        Console.WriteLine("Managed Code Example.");
    }
}

8. What is Unmanaged Code?

• Unmanaged Code is code executed directly by the operating system, not under the control of CLR.
• Examples include applications written in C or C++ that are compiled directly into machine code.

Example:

// Calling unmanaged code from C#
[DllImport("User32.dll")]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, int options);

9. What is the difference between Value Types and Reference Types in .NET?

• Value Types:
  • Stored directly in memory.
  • Examples: int, float, bool.
• Reference Types:
  • Store a reference (pointer) to the actual data in memory.
  • Examples: class, object, string.

Example:

// Value type
int x = 10;

// Reference type
string name = "John";

10. What is Boxing and Unboxing in .NET?

• Boxing: Converting a value type to an object (reference type).
• Unboxing: Extracting the value type from an object.

Example:

// Boxing
int num = 123;
object obj = num;  // Boxing

// Unboxing
int unboxedNum = (int)obj;  // Unboxing

 

11. What is the Common Type System (CTS)?

• CTS defines all data types in the .NET Framework and how they are represented in memory.
• It ensures that data types used across different .NET languages (C#, VB.NET, F#) are compatible with each other.
• Value Types (stored in the stack) and Reference Types (stored in the heap) are both part of CTS.

Example:

// Value type
int valueType = 100;

// Reference type
string referenceType = "Hello";

12. What is the Common Language Specification (CLS)?

• CLS defines a subset of the Common Type System (CTS) that all .NET languages must follow to ensure cross-language compatibility.
• It provides a set of rules for data types and programming constructs that are guaranteed to work across different languages.

Example:

 // CLS-compliant code: using standard types
public class SampleClass
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

 

13. What is Just-In-Time (JIT) Compilation?

• JIT Compilation is a process where the Intermediate Language (IL) code is converted to machine code at runtime.
• It helps optimize execution by compiling code only when it is needed, thus saving memory and resources.

Types of JIT Compilers:

• Pre-JIT: Compiles the entire code during deployment.
• Econo-JIT: Compiles only required methods, reclaims memory afterward.
• Normal JIT: Compiles methods when called for the first time.

 

 

14. What is the difference between Early Binding and Late Binding in .NET?

• Early Binding:

  • Happens at compile time.
  • Compiler knows the method signatures and types in advance.
  • Safer and faster.

• Late Binding:

  • Happens at runtime.
  • Uses reflection to dynamically invoke methods and access types.
  • Flexible but slower and prone to errors.

Example:

 // Early binding
SampleClass obj = new SampleClass();
obj.PrintMessage();

// Late binding using reflection
Type type = Type.GetType("SampleClass");
object instance = Activator.CreateInstance(type);
MethodInfo method = type.GetMethod("PrintMessage");
method.Invoke(instance, null);

 

15. What is Garbage Collection (GC) in .NET?

• Garbage Collection is the process in the .NET Framework that automatically frees memory by reclaiming objects that are no longer in use.
• GC improves memory management by cleaning up unreferenced objects.

Generations in Garbage Collection:

1. Generation 0: Short-lived objects.
2. Generation 1: Medium-lived objects.
3. Generation 2: Long-lived objects.

Example:

 class Program
{
    static void Main()
    {
        // Force garbage collection
        GC.Collect();
        GC.WaitForPendingFinalizers();
    }
}

 

16. What is the difference between Dispose() and Finalize()?

• Dispose():
  • Part of the IDisposable interface.
  • Must be called explicitly to release unmanaged resources.
• Finalize():
  • Called by the Garbage Collector before an object is destroyed.
  • Cannot be called explicitly; handled by the system.

Example:

 class MyClass : IDisposable
{
    public void Dispose()
    {
        // Clean up unmanaged resources
    }
    
    ~MyClass()
    {
        // Finalizer (destructor) called by GC
    }
}

 

17. What is Reflection in .NET?

• Reflection allows programs to inspect and interact with object metadata at runtime.
• It can be used to dynamically create instances, invoke methods, and access fields and properties.

Example:

 Type type = typeof(SampleClass);
object instance = Activator.CreateInstance(type);
MethodInfo method = type.GetMethod("PrintMessage");
method.Invoke(instance, null);

 

18. What is ADO.NET?

• ADO.NET is a data access technology used to interact with databases (SQL, Oracle, etc.) in the .NET Framework.
• It provides data connectivity between .NET applications and data sources, allowing you to execute SQL queries, stored procedures, and manage transactions.

Components of ADO.NET:

• Connection: Establishes a connection to the database.
• Command: Executes SQL statements.
• DataReader: Reads data from a data source in a forward-only manner.
• DataAdapter: Fills DataSet/DataTable with data.
• DataSet/DataTable: In-memory representation of data.

Example:

 using (SqlConnection connection = new SqlConnection("connectionString"))
{
    SqlCommand command = new SqlCommand("SELECT * FROM Students", connection);
    connection.Open();
    
    SqlDataReader reader = command.ExecuteReader();
    while (reader.Read())
    {
        Console.WriteLine(reader["Name"]);
    }
}

19. What is the difference between DataReader and DataSet in ADO.NET?

• DataReader:
  • Provides forward-only, read-only access to data from a database.
  • Faster and more memory-efficient.
• DataSet:
  • In-memory representation of data that can be manipulated without being connected to the database.
  • Slower, but supports multiple tables and relationships.

 

 

20. What is ASP.NET?

• ASP.NET is a web application framework developed by Microsoft for building dynamic web pages, websites, and web services.
• It provides tools and libraries for building web applications with features like state management, server controls, and web forms.

Types of ASP.NET Applications:

• Web Forms: Event-driven development model with server-side controls.
• MVC (Model-View-Controller): A design pattern separating data, UI, and logic.
• Web API: Used for building RESTful web services.
• Blazor: Allows building interactive web UIs using C# instead of JavaScript.

Example (Web Forms):

 protected void Button_Click(object sender, EventArgs e)
{
    Label.Text = "Hello, ASP.NET!";
}

 

21. What are HTTP Handlers and HTTP Modules in ASP.NET?

• HTTP Handlers:

  • Low-level components that process incoming HTTP requests directly.
  • Typically used to handle requests for specific file types (e.g., .aspx, .ashx).

• HTTP Modules:

  • Intercepts and modifies requests/responses at various stages in the pipeline.
  • Used for authentication, logging, or custom headers.

Example (Handler):

 public class MyHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";
        context.Response.Write("Handled by MyHandler.");
    }
    
    public bool IsReusable => false;
}

 

22. What is the difference between Session and ViewState in ASP.NET?

• Session:
  • Stores user-specific data on the server.
  • Persists across multiple pages and requests within a session.
  • Consumes more server resources (memory).
• ViewState:
  • Stores data in a hidden field on the client (browser) side.
  • Retains data only for a single page during postbacks.
  • Increases page size but doesn’t use server memory.

Example of ViewState:

 // Storing value in ViewState
ViewState["UserName"] = "John";

// Retrieving value from ViewState
string userName = ViewState["UserName"].ToString();

 

23. What is ASP.NET MVC?

• ASP.NET MVC is a web development framework that follows the Model-View-Controller design pattern.
  • Model: Represents the application data and business logic.
  • View: Displays the data and the user interface.
  • Controller: Handles user input, updates the model, and selects a view to render.

Advantages:

• Separation of concerns.
• Easier unit testing.
• Greater control over HTML, CSS, and JavaScript.

Example:

 public class HomeController : Controller
{
    public ActionResult Index()
    {
        return View();
    }
}

 

24. What are Action Filters in ASP.NET MVC?

• Action Filters allow you to execute code before or after an action method is executed.
• Common use cases include logging, authorization, and caching.

Types of Action Filters:

• Authorization Filters (e.g., Authorize).
• Action Filters (e.g., OnActionExecuting, OnActionExecuted).
• Result Filters (e.g., OnResultExecuting, OnResultExecuted).
• Exception Filters (e.g., HandleError).

Example:

 public class LogActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // Log before action executes
    }
}

 

25. What is Entity Framework (EF)?

• Entity Framework is an Object-Relational Mapping (ORM) framework for .NET that allows developers to work with databases using .NET objects (classes) instead of writing SQL queries.
• Advantages:
  • Automatic generation of database schema.
  • Enables LINQ to query the database.
  • Database migration support for schema changes.

Example:

 // Defining a model
public class Student
{
    public int ID { get; set; }
    public string Name { get; set; }
}

// Using Entity Framework to interact with the database
using (var context = new SchoolContext())
{
    var students = context.Students.ToList();
}

26. What is the difference between LINQ to SQL and Entity Framework?

• LINQ to SQL:
  • Designed for direct database access with SQL Server.
  • Supports a one-to-one mapping between database tables and .NET classes.
  • Simpler but less feature-rich than Entity Framework.
• Entity Framework (EF):
  • Provides more features such as inheritance, complex types, and multi-table mapping.
  • Works with multiple database providers (SQL Server, MySQL, Oracle).
  • Supports Code First, Database First, and Model First approaches.

 

 

27. What is Web API in ASP.NET?

• ASP.NET Web API is a framework for building HTTP-based services that can be consumed by a wide variety of clients (e.g., browsers, mobile devices).
• Web API is primarily used to create RESTful services, where HTTP verbs (GET, POST, PUT, DELETE) map to CRUD operations.

 public class ProductsController : ApiController
{
    public IEnumerable<Product> GetAllProducts()
    {
        return productList;
    }
}

 

28. What is Dependency Injection (DI) in ASP.NET?

• Dependency Injection is a design pattern that allows injecting objects into a class, rather than creating objects inside the class.
• It decouples the creation of objects from the business logic, making the code more modular and testable.

Example (using ASP.NET Core DI):

 public class HomeController : Controller
{
    private readonly IProductService _productService;
    
    public HomeController(IProductService productService)
    {
        _productService = productService;
    }
    
    public IActionResult Index()
    {
        var products = _productService.GetProducts();
        return View(products);
    }
}

 

29. What are REST and SOAP?

• REST (Representational State Transfer):

  • Uses HTTP methods (GET, POST, PUT, DELETE).
  • Stateless communication.
  • JSON or XML as data format.
  • Simpler and more scalable for web APIs.

• SOAP (Simple Object Access Protocol):

  • Uses XML for request and response messages.
  • Requires more overhead due to its strict structure and protocols.
  • Supports security features like WS-Security.

 

 

30. What is OAuth in ASP.NET?

• OAuth is an open standard for token-based authentication, used to grant third-party applications limited access to user resources without exposing credentials.
• OAuth is commonly used in social logins (e.g., login with Google or Facebook).

31. What is SignalR in ASP.NET?

• SignalR is a library that allows real-time web functionality in ASP.NET applications.
• It enables the server to send updates to clients instantly via WebSockets, long-polling, or Server-Sent Events.

Use cases:

• Chat applications.
• Real-time notifications.
• Live data feeds.

Example:

 public class ChatHub : Hub
{
    public async Task SendMessage(string user, string message)
    {
        await Clients.All.SendAsync("ReceiveMessage", user, message);
    }
}

 

32. What is NuGet in .NET?

• NuGet is a package manager for .NET, allowing developers to share and consume reusable code libraries.
• It simplifies the process of including third-party libraries into your project.

Example:

 Install-Package Newtonsoft.Json

 

33. What are Generics in C#?

• Generics allow defining classes, interfaces, and methods with placeholders for data types.
• They promote code reusability and type safety by allowing you to create type-agnostic data structures.

Example:

 public class GenericClass<T>
{
    public T Data { get; set; }
}

 

34. What is a delegate in C#?

• Delegates are type-safe function pointers that allow methods to be passed as parameters.
• Useful in implementing callback functions, events, and asynchronous programming.

Example:

 public delegate void DisplayMessage(string message);

public void ShowMessage(string message)
{
    Console.WriteLine(message);
}

DisplayMessage display = new DisplayMessage(ShowMessage);
display("Hello, World!");

 

35. What are events in C#?

• Events provide a mechanism for a class to notify other classes or objects when something of interest occurs.
• Events are built on top of delegates and are typically used in UI programming and handling user interactions.

Example:

 public event EventHandler ButtonClicked;

 

36. What are Extension Methods in C#?

• Extension Methods allow you to add new methods to existing types without modifying their source code or creating a derived type.
• Extension methods are static methods, but they are called as if they were instance methods on the extended type.

Syntax:

 public static class StringExtensions
{
    public static int WordCount(this string str)
    {
        return str.Split(' ').Length;
    }
}

// Usage
string sentence = "Hello World";
int count = sentence.WordCount();  // Output: 2

Key Points:

• Defined in static classes.
• The first parameter specifies the type being extended, and the keyword this is used before the type.

 

37. What is the difference between finalize and dispose methods?

• Finalize:

  • Called by the garbage collector before an object is destroyed.
  • Used to release unmanaged resources.
  • Cannot be called explicitly in code.
  • Defined using a destructor in C#.

• Dispose:

  • Explicitly called by the developer to release unmanaged resources.
  • Part of the IDisposable interface.
  • Should be used when working with resources like file handles or database connections.

Example using Dispose:

 public class ResourceHolder : IDisposable
{
    private bool disposed = false;
    
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }
    
    protected virtual void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                // Free managed resources
            }
            // Free unmanaged resources
            disposed = true;
        }
    }
    
    ~ResourceHolder()
    {
        Dispose(false);
    }
}

 

38. What is the using statement in C#?

• The using statement is used to automatically manage the disposal of unmanaged resources.
• It ensures that Dispose() is called on objects that implement IDisposable, even if an exception occurs.

Example:

 using (var reader = new StreamReader("file.txt"))
{
    string content = reader.ReadToEnd();
}
// `Dispose()` is automatically called on `StreamReader`.

 

39. What is a sealed class in C#?

• A sealed class cannot be inherited by other classes. It restricts the class hierarchy by preventing inheritance.
• Sealing a class can be useful for security, performance, or if you want to ensure the class’s implementation stays unchanged.

Example:

 public sealed class SealedClass
{
    public void Display()
    {
        Console.WriteLine("This is a sealed class.");
    }
}

 

40. What is the lock statement in C#?

• The lock statement is used to ensure that a block of code is executed by only one thread at a time. It provides thread-safety by preventing race conditions.
• Typically used when working with shared resources in multi-threaded applications.

Example:

 private static object _lock = new object();

public void CriticalSection()
{
    lock (_lock)
    {
        // Code that must be synchronized
    }
}

 

41. What are Indexers in C#?

• Indexers allow objects to be indexed like arrays. They enable a class to be accessed using square brackets [], similar to array elements.

Example:

 public class SampleCollection
{
    private string[] elements = new string[100];
    
    public string this[int index]
    {
        get { return elements[index]; }
        set { elements[index] = value; }
    }
}

// Usage
SampleCollection collection = new SampleCollection();
collection[0] = "First Element";
Console.WriteLine(collection[0]); // Output: First Element

 

42. What is the difference between Array and ArrayList in C#?

• Array:

  • Fixed size, strongly-typed (can only hold one data type).
  • Faster performance due to strong typing.

• ArrayList:

  • Dynamic size, but not strongly-typed (can hold different data types).
  • Uses more memory and is slower compared to arrays due to boxing and unboxing of value types.

Example:

 // Array
int[] numbers = new int[5];

// ArrayList
ArrayList list = new ArrayList();
list.Add(1);
list.Add("String"); // Mixed types

 

43. What is a Multicast Delegate in C#?

• A Multicast Delegate can hold references to multiple methods. When invoked, it calls all the methods in its invocation list.

Example:

 public delegate void Notify();

public class DelegateExample
{
    public static void Method1() { Console.WriteLine("Method1"); }
    public static void Method2() { Console.WriteLine("Method2"); }

    public static void Main()
    {
        Notify notifyDelegate = Method1;
        notifyDelegate += Method2; // Multicast
        notifyDelegate.Invoke();
    }
}

// Output:
// Method1
// Method2

 

44. What is the difference between IEnumerable and IQueryable in C#?

• IEnumerable:

  • Suitable for in-memory data collection.
  • Queries are executed in memory.
  • Supports LINQ to Objects and LINQ to XML.

• IQueryable:

  • Suitable for out-of-memory data (e.g., databases).
  • Queries are executed on the data source (e.g., SQL database).
  • Supports deferred execution and LINQ to SQL.

Example:

 // Using IQueryable for deferred execution
IQueryable<Product> query = dbContext.Products.Where(p => p.Price > 50);

// Using IEnumerable
IEnumerable<Product> products = query.ToList();

 

45. What are anonymous methods in C#?

• Anonymous methods allow you to define inline, unnamed methods using the delegate keyword.
• They are used for shorter, simpler delegate expressions, and can capture variables from their surrounding scope.

Example:

 Func<int, int> square = delegate (int x)
{
    return x * x;
};

int result = square(5);  // Output: 25

 

46. What are Lambda Expressions in C#?

• Lambda expressions are concise ways to write anonymous methods. They are used extensively in LINQ queries.

Example:

 Func<int, int> square = x => x * x;

int result = square(5);  // Output: 25

 

47. What is the role of yield in C#?

• yield allows methods to return elements of a collection one at a time, without storing them all in memory. It's useful for creating custom iterator methods.

Example:

 public IEnumerable<int> GetNumbers()
{
    for (int i = 1; i <= 5; i++)
    {
        yield return i;
    }
}

// Usage
foreach (int number in GetNumbers())
{
    Console.WriteLine(number);
}

 

48. What is Reflection in C#?

• Reflection allows inspecting and interacting with the metadata of types, methods, and properties at runtime.

Use cases:

• Creating objects dynamically.
• Invoking methods at runtime.
• Accessing private fields and methods.

Example:

 Type type = typeof(MyClass);
MethodInfo method = type.GetMethod("MyMethod");
method.Invoke(Activator.CreateInstance(type), null);

 

49. What is the purpose of is and as operators in C#?

• is: Checks if an object is of a specific type.
• as: Attempts to cast an object to a specific type, returning null if the cast fails.

Example:

 object obj = "Hello";

if (obj is string)
{
    string str = obj as string;
    Console.WriteLine(str);
}

 

50. What is the out keyword in C#?

• The out keyword allows a method to return multiple values by passing arguments by reference.
• Parameters marked with out must be assigned a value before the method returns.

Example:

 public void GetValues(out int a, out int b)
{
    a = 10;
    b = 20;
}

// Usage
int x, y;
GetValues(out x, out y);
Console.WriteLine($"x = {x}, y = {y}");

 

51. What is a Strong Name in .NET?

• A Strong Name uniquely identifies an assembly using its name, version, culture, and public key token.
• Strongly named assemblies are stored in the GAC and help in avoiding conflicts between versions.

Example:

 sn -k MyKey.snk

 

52. What is the difference between const and readonly in C#?

• const:
  • Compile-time constant.
  • Value cannot change.
  • Must be assigned at declaration.
• readonly:
  • Runtime constant.
  • Can be assigned at runtime in the constructor.

Example:

 const int maxItems = 100;
readonly int maxLimit;

 

53. What is the purpose of sealed methods in C#?

• A sealed method is a method that prevents overriding in derived classes.
• Only applies to methods in base classes marked virtual or override.

Example:

 public override sealed void Method()
{
    // This method cannot be overridden further.
}

 

54. What is the difference between throw and throw ex in exception handling?

• throw: Re-throws the original exception while preserving the stack trace.
• throw ex: Resets the stack trace, making it harder to trace the original error.

Example:

 try
{
    // Some code
}
catch(Exception ex)
{
    throw; // Preserves original exception
}

 

55. What is the difference between Task and Thread in C#?

• Task: Higher-level abstraction for managing asynchronous operations. It supports continuations and better integrates with async/await.
• Thread: Lower-level, represents a unit of execution in the system.

 

 

56. What is Lazy<T> in C#?

• Lazy<T> provides a way to delay the initialization of an object until it is needed (lazy loading).

Example:

 Lazy<MyClass> lazyObj = new Lazy<MyClass>(() => new MyClass());

 

57. What is the difference between Abstract Class and Interface in C#?

• Abstract Class:
  • Can have method implementations.
  • Supports access modifiers.
  • Can contain constructors.
• Interface:
  • Only method declarations (before C# 8.0).
  • Cannot have access modifiers.
  • No constructors.

 

58. What is the difference between synchronous and asynchronous programming?

• Synchronous:
  • Blocking, one operation must complete before another can start.
• Asynchronous:
  • Non-blocking, allows operations to run in parallel or independently.

Example:

 await Task.Delay(1000); // Asynchronous call

 

59. What is the Func delegate in C#?

• Func is a built-in delegate type that returns a value. It can take up to 16 input parameters.

Example:

 Func<int, int, int> add = (x, y) => x + y;

 

60. What is the difference between String and StringBuilder?

• String: Immutable, every change creates a new string object.
• StringBuilder: Mutable, optimized for multiple manipulations on strings.

 

 

61. What is the Singleton Design Pattern?

• The Singleton Pattern ensures that a class has only one instance and provides a global point of access to it.

Example:

 public class Singleton
{
    private static Singleton _instance;
    private Singleton() { }

    public static Singleton Instance => _instance ??= new Singleton();
}

 

62. What is Memory Leak in .NET and how to prevent it?

• A Memory Leak occurs when objects are no longer used but not freed, causing memory exhaustion.
• To prevent it:
  • Dispose unmanaged resources properly.
  • Use weak references where applicable.
  • Implement the IDisposable interface.

 

63. What is the difference between Task.Run() and TaskFactory.StartNew()?

• Task.Run(): Suitable for CPU-bound operations and preferred for new code.
• TaskFactory.StartNew(): Offers more configuration options and is more flexible.

 

64. What is the volatile keyword in C#?

• The volatile keyword ensures that a variable's value is always read from memory, preventing optimizations that might cache its value in CPU registers.

 

65. What is the difference between Task.Wait() and Task.Result?

• Task.Wait(): Blocks the calling thread until the task completes.
• Task.Result: Blocks the thread and retrieves the task’s result.

 

66. What is the difference between a Shallow Copy and a Deep Copy?

• Shallow Copy: Copies the reference types as references (pointers).
• Deep Copy: Copies the actual objects, creating new instances.

 

67. What is the difference between a List<T> and an Array in C#?

• List<T>: Dynamic size, resizable, part of System.Collections.Generic.
• Array: Fixed size, cannot resize after creation.

 

68. What are Nullable Types in C#?

• Nullable types allow value types to have null values, using the ? syntax.

Example:

 int? num = null;

 

69. What is the difference between First() and FirstOrDefault() in LINQ?

• First(): Throws an exception if no element is found.
• FirstOrDefault(): Returns a default value (like null or 0) if no element is found.

 

70. What is yield in C#?

• yield is used to create an iterator block, returning each element of a collection one at a time without creating the entire collection in memory.

 

71. What are the differences between Task and ThreadPool?

• Task: Used for managing parallel code.
• ThreadPool: Manages a pool of worker threads to perform tasks.

 

72. What is the lock keyword in C#?

• lock is used to ensure that a block of code runs exclusively in a multi-threaded environment, preventing race conditions.

 

73. What is IEnumerable<T> in C#?

• IEnumerable<T> represents a forward-only, read-only collection of a sequence of elements.

 

 

74. What is Covariance and Contravariance in C#?

• Covariance allows a method to return a more derived type than the specified type.
• Contravariance allows a method to accept arguments of a more general type than the specified type.

 

75. What is a Mutex in .NET?

• A Mutex is used for synchronizing access to a resource across multiple threads and processes.

 

76. What are Tuples in C#?

• A Tuple is a data structure that can hold multiple values of different types.

Example:

 var tuple = Tuple.Create(1, "Hello", true);

 

77. What is the difference between ToString() and Convert.ToString()?

• ToString(): Can throw an exception if the object is null.
• Convert.ToString(): Returns an empty string if the object is null.

 

78. What is the ThreadLocal<T> class in C#?

• ThreadLocal<T> provides thread-local storage, meaning each thread has its own separate instance of a variable.

 

79. What is the ICloneable interface in C#?

• The ICloneable interface provides a mechanism for creating a copy of an object.

 

80. What is the WeakReference class in C#?

• A WeakReference allows an object to be garbage collected while still allowing a reference to the object.

 

 

 

How to copy MySQL data from one database to another database in .net core?

MySQL backup and restore some times become hack-trick task because of unnecessary lines on code generated when exporting data from mysql workbench in individual file for tables. It becomes harder if there are large number of tables.

Following is a sample console application that will copy data from a source database table and bulk insert to a destination database table. It loops through all tables and perform the data transfer of all tables.

Install MySQLConnection nuget package.

using MySqlConnector;
using System.Data;


string schemaName = "db_dev";
string sourceConnectionString = "server=srchost;user id=admin;password=mypwd;persistsecurityinfo=True;database=db_dev;";
string destinationConnectionString = "server=desthost;user id=myadmin;password=mypass;persistsecurityinfo=True;database=destdb_dev;AllowLoadLocalInfile=true;";


int i = 0;
using (MySqlConnection sourceConnection = new MySqlConnection(sourceConnectionString))
{
    sourceConnection.Open();

    // Get the list of tables in the source database
    DataTable tables = sourceConnection.GetSchema("Tables");
    DataTable filteredRows = tables.Select($"TABLE_SCHEMA = '{schemaName}'").CopyToDataTable();
    foreach (DataRow row in filteredRows.Rows)
    {
        string tableName = row[2].ToString();
        int dataCount = Convert.ToInt32(row[7].ToString());
        i++;
        // Read data from the source table
        string selectQuery = $"SELECT * FROM `{schemaName}`.`{tableName}`";
        MySqlCommand selectCommand = new MySqlCommand(selectQuery, sourceConnection);
        if (dataCount > 0 && i>=0)
            using (MySqlDataReader reader = selectCommand.ExecuteReader())
            {
                var rows = reader.HasRows;
                using (MySqlConnection destinationConnection = new MySqlConnection(destinationConnectionString))
                {
                    destinationConnection.Open();

                    // Prepare the bulk insert command
                    using (MySqlTransaction transaction = destinationConnection.BeginTransaction())
                    {
                        MySqlBulkCopy bulkCopy = new MySqlBulkCopy(destinationConnection, transaction);
                        bulkCopy.DestinationTableName = tableName;
                        try
                        {
                            // Bulk insert data into the destination table
                            bulkCopy.WriteToServer(reader);
                            transaction.Commit();
                            Console.WriteLine($"Data from table {tableName} has been successfully transferred." +i.ToString());
                        }
                        catch (Exception ex)
                        {
                            transaction.Rollback();
                            Console.WriteLine($"Error transferring data from table {tableName}: {ex.Message}");
                        }
                    }
                }
            }
    }
}


Console.WriteLine("Hello, World!");

 

 

 

 

 

 

 

 

 

How do you implement background processing and message queues in a .NET Core Web API?

Background processing and message queues are important aspects of a .NET Core Web API that allow for asynchronous and distributed processing. Here are some steps to implement them:

1. Choose a message queue system: There are several message queue systems available, such as RabbitMQ, Azure Service Bus, and AWS SQS. Choose the one that best suits your needs.
2. Install the required packages: Depending on the message queue system you choose, install the necessary packages, such as RabbitMQ.Client or Microsoft.Azure.ServiceBus.
3. Implement message producers and consumers: Create classes that implement message producers and consumers. A message producer is responsible for sending messages to the queue, while a message consumer receives messages from the queue and processes them.
4. Configure the message queue system: Configure the message queue system, such as setting up queues, topics, and subscriptions, and configuring access policies and security.
5. Implement background processing: Use a message queue system to implement background processing. For example, you can use a message producer to send a message to a queue, which is then processed by a message consumer in the background.
6. Handle message retries and failures: Implement logic to handle message retries and failures, such as implementing an exponential backoff algorithm to retry failed messages.
7. Monitor message queue metrics: Monitor message queue metrics, such as queue length, message processing time, and message failure rate, to ensure optimal performance and reliability.

By following these steps, you can implement background processing and message queues in your .NET Core Web API to improve its performance and scalability.

What are some best practices for logging and monitoring a .NET Core Web API?

Here are some best practices for logging and monitoring a .NET Core Web API:

1. Use a centralized logging system: Instead of relying on individual log files on each server, use a centralized logging system to aggregate logs from all servers. This makes it easier to search and analyze logs.
2. Use structured logging: Structured logging involves logging data in a structured format such as JSON or XML. This makes it easier to search and analyze logs.
3. Log all errors and exceptions: Log all errors and exceptions, including the stack trace, to help with debugging and troubleshooting.
4. Implement logging at different levels: Implement logging at different levels, such as debug, info, warning, and error, to help with troubleshooting and monitoring.
5. Use log correlation: Use a unique identifier in each log message to track the flow of requests through your system. This makes it easier to diagnose problems that span multiple services.
6. Monitor performance metrics: Monitor performance metrics such as response time, throughput, and error rates to identify and troubleshoot performance issues.
7. Set up alerts: Set up alerts to notify you when errors or performance issues occur. This enables you to respond quickly and minimize downtime.
8. Use application performance monitoring (APM) tools: APM tools provide real-time visibility into the performance of your application and its dependencies. They can help you identify and troubleshoot performance issues more quickly.
9. Implement security monitoring: Implement security monitoring to detect and respond to potential security threats. This includes monitoring for unusual login attempts, unauthorized access attempts, and other suspicious activity.
10. Regularly review logs and metrics: Regularly review logs and metrics to identify trends and areas for improvement. This can help you optimize performance and prevent issues before they occur.

How do you implement SSL/TLS encryption in a .NET Core Web API?

SSL/TLS encryption is essential for securing web applications by encrypting the data transmitted between the client and server. In a .NET Core Web API, you can implement SSL/TLS encryption by following these steps:

1. Obtain a certificate: To use SSL/TLS encryption, you need to obtain a certificate. You can either purchase a certificate from a trusted third-party provider or create a self-signed certificate.
2. Configure HTTPS in your application: Once you have obtained a certificate, you need to configure HTTPS in your application. You can do this by modifying the launchSettings.json file or adding the UseHttpsRedirection and UseHsts methods in the Startup.cs file.
3. Redirect HTTP requests to HTTPS: To ensure that all requests are encrypted, you can redirect HTTP requests to HTTPS. You can do this by adding the UseHttpsRedirection method in the Startup.cs file.
4. Configure SSL/TLS in your server: You need to configure your server to use SSL/TLS. This can be done by modifying the web server configuration file.
5. Test your SSL/TLS implementation: Finally, you should test your SSL/TLS implementation to ensure that it is working correctly.

Overall, SSL/TLS encryption is a crucial component of web application security, and it is essential to implement it correctly in a .NET Core Web API.

What is the role of serialization and deserialization in a .NET Core Web API, and how do you implement it?

Serialization and deserialization are essential processes in a .NET Core Web API, as they allow the conversion of data between different formats, such as JSON or XML, and .NET Core objects.

Serialization is the process of converting an object into a format that can be transmitted or stored, such as JSON or XML. This process is commonly used in a Web API when returning data to a client.

Deserialization is the opposite process, which converts the data back into .NET Core objects.

To implement serialization and deserialization in a .NET Core Web API, you can use the built-in JSON serializer, which is included in the Microsoft.AspNetCore.Mvc.NewtonsoftJson package. This package allows you to easily convert .NET Core objects to and from JSON format.

To use the JSON serializer, you can add the AddNewtonsoftJson() extension method to the ConfigureServices method in the Startup.cs file, as follows:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers()
            .AddNewtonsoftJson();
}


This registers the JSON serializer as the default serializer for the Web API.

You can also customize the JSON serializer settings by passing an instance of the JsonSerializerSettings class to the AddNewtonsoftJson() method. For example, to specify that null values should be included in the JSON output, you can do the following:

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers()
            .AddNewtonsoftJson(options => {
                options.SerializerSettings.NullValueHandling = NullValueHandling.Include;
            });
}


Serialization and deserialization are essential processes in a .NET Core Web API, and using the built-in JSON serializer can make it easy to convert .NET Core objects to and from JSON format.

How do you implement load balancing and failover in a .NET Core Web API?

Load balancing and failover are critical components of building scalable and highly available applications. In a .NET Core Web API, load balancing can be achieved by distributing incoming requests across multiple instances of the API, while failover ensures that if one instance fails, the remaining instances can continue serving requests.

Here are the steps to implement load balancing and failover in a .NET Core Web API:

1. Set up multiple instances of your .NET Core Web API: You can create multiple instances of your .NET Core Web API on different servers or using containers.
2. Configure a load balancer: The load balancer can distribute incoming requests across the different instances of the Web API. You can use a software load balancer like NGINX or HAProxy.
3. Implement health checks: Your load balancer should periodically check the health of each instance of the Web API. If an instance fails, the load balancer should stop sending traffic to that instance until it is restored.
4. Implement session affinity: If your Web API uses sessions, you will need to ensure that requests from a user are always directed to the same instance of the Web API. This is known as session affinity or sticky sessions.
5. Implement a failover mechanism: If one instance of the Web API fails, your load balancer should be able to redirect traffic to the remaining healthy instances.
6. Monitor the system: You should monitor the system to ensure that the load balancer is distributing traffic correctly and that instances are healthy.

Overall, load balancing and failover are critical for ensuring that your .NET Core Web API can handle high traffic and remain available even in the event of a failure. By implementing these mechanisms, you can provide a better user experience and ensure that your application is reliable and scalable.

How do you implement logging in a .NET Core Web API?

Logging is an essential part of any application, and it can help in debugging issues and analyzing the behavior of an application. In a .NET Core Web API, you can implement logging by using the built-in logging framework provided by the .NET Core runtime.

To implement logging in a .NET Core Web API, you can follow these steps:

• Add the logging framework: First, you need to add the logging framework to your .NET Core Web API project. You can do this by adding the Microsoft.Extensions.Logging NuGet package.
• Configure logging: You can configure logging by using the ConfigureLogging method in the WebHostBuilder class. In this method, you can specify the logging providers that you want to use, such as the console, file, or database.
• Inject the logger: In your controller or service classes, you can inject the logger by adding it to the constructor. You can use the ILogger interface to log messages at different levels, such as information, warning, and error.
• Log messages: Once you have injected the logger, you can use it to log messages at different levels. For example, you can use the LogInformation method to log an informational message, or the LogError method to log an error message.

Here's an example of how to use the logging framework in a .NET Core Web API:

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;

namespace MyWebApi.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class MyController : ControllerBase
    {
        private readonly ILogger<MyController> _logger;

        public MyController(ILogger<MyController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IActionResult Get()
        {
            _logger.LogInformation("Request received");
            // do some work
            _logger.LogInformation("Request processed successfully");
            return Ok();
        }
    }
}


In this example, we inject the ILogger interface into the MyController class, and use it to log an informational message when a request is received, and another informational message when the request is processed successfully.

By default, the logging framework logs messages to the console, but you can also configure it to log messages to other destinations, such as a file or a database, by adding the appropriate provider.

What is the role of middleware in a .NET Core Web API, and how do you use it?

Middleware is a key component in the pipeline of a .NET Core Web API that allows developers to add custom logic to the processing of requests and responses. Middleware functions as a "chain" of components, where each component is responsible for executing a specific task in the pipeline.

Middleware can be used for a variety of purposes, such as:

1. Authentication and authorization
2. Request and response logging
3. Caching
4. Exception handling
5. Compression and response size reduction
6. Custom header and response modification
7. Routing and URL rewriting

Middleware is added to the pipeline by using the Use method of the IApplicationBuilder interface. Middleware can be added to the pipeline in the Startup.cs file of the project. The order in which middleware is added to the pipeline is important, as it determines the order in which the middleware will be executed.

For example, to add middleware for logging requests and responses, the following code can be added to the Configure method in Startup.cs:

app.Use(async (context, next) =>
{
    // Log request details
    Console.WriteLine($"{context.Request.Method} {context.Request.Path}");

    // Call the next middleware in the pipeline
    await next();

    // Log response details
    Console.WriteLine($"Response status code: {context.Response.StatusCode}");
});
 

This middleware will log the request method and path, execute the next middleware in the pipeline, and then log the response status code.

Overall, middleware is a powerful tool in a .NET Core Web API that allows developers to add custom logic to the processing of requests and responses in a flexible and extensible manner.

 

 

 

How do you handle concurrency and locking in a .NET Core Web API?

 Concurrency and Locking Concepts:

Concurrency and locking are important concepts in web development as multiple requests can be made to a web application at the same time. In a .NET Core Web API, concurrency can be handled using various techniques, such as optimistic concurrency, pessimistic concurrency, and locking.

Optimistic concurrency is a technique that assumes that conflicts between concurrent transactions are rare. In this technique, each transaction reads data from the database and then modifies it. Before committing the transaction, it checks whether the data has been modified by another transaction. If the data has been modified, the transaction is rolled back and the user is notified.

Pessimistic concurrency is a technique that assumes that conflicts between concurrent transactions are likely. In this technique, a lock is placed on the data being modified to prevent other transactions from modifying it at the same time. This can lead to decreased performance, as it can result in increased waiting time for other transactions.

Locking is a technique that can be used in both optimistic and pessimistic concurrency. In optimistic concurrency, a lock can be placed on the data being modified to prevent other transactions from modifying it at the same time. In pessimistic concurrency, a lock is placed on the data being modified to prevent other transactions from modifying it at the same time. This can result in decreased performance, as it can result in increased waiting time for other transactions.

To handle concurrency and locking in a .NET Core Web API, you can use various techniques, such as the lock keyword, the ReaderWriterLockSlim class, and the ConcurrentDictionary class. You can also use database-specific features, such as row versioning in SQL Server, to handle concurrency.

Different ways of concurrent programming in .net core:

Concurrency is an important aspect of modern software development, and .NET Core provides various mechanisms to implement concurrency. Here are some ways to implement concurrency in .NET Core:

Asynchronous Programming: 

Asynchronous programming allows you to perform long-running operations without blocking the main thread of your application. This can be achieved using the async and await keywords in C#. Here is an example of how to use asynchronous programming to fetch data from a remote API:

public async Task<string> GetDataAsync()

{

    using (var httpClient = new HttpClient())

    {

        var response = await httpClient.GetAsync("https://api.example.com/data");

        return await response.Content.ReadAsStringAsync();

    }

}

Parallel Programming: 

Parallel programming allows you to execute multiple tasks simultaneously on different threads. This can be achieved using the Parallel class in .NET Core. Here is an example of how to use parallel programming to perform CPU-bound tasks:

public void PerformTasksInParallel()

{

    var tasks = new List<Task>();

    for (int i = 0; i < 10; i++)

    {

        tasks.Add(Task.Run(() =>

        {

            // Perform CPU-bound task here

        }));

    }

    Task.WaitAll(tasks.ToArray());

}

Task Parallel Library (TPL): 

The Task Parallel Library (TPL) is a powerful framework for concurrent programming in .NET Core. TPL provides a set of classes and methods for performing parallel operations, including parallel loops, data parallelism, and task coordination. Here is an example of how to use TPL to perform parallel loops:

public void PerformParallelLoop()

{

    var numbers = Enumerable.Range(1, 100);

    Parallel.ForEach(numbers, (number) =>

    {

        // Perform operation on each number in parallel

    });

}

Concurrent Collections: 

Concurrent collections are thread-safe collections that can be accessed by multiple threads concurrently without the need for locks or other synchronization mechanisms. This can improve performance and reduce the risk of deadlocks and other synchronization issues. Here is an example of how to use a concurrent dictionary to store data in a thread-safe manner:

private readonly ConcurrentDictionary<int, string> _data = new ConcurrentDictionary<int, string>();

public void AddData(int key, string value)

{

    _data.TryAdd(key, value);

}

Different ways of Locking implementation in .net core:

Locking is a mechanism to ensure that only one thread at a time can access a shared resource in a multi-threaded environment. .NET Core provides several ways to implement locking, including the lock statement, the Monitor class, and the ReaderWriterLockSlim class. Here are some examples of how to use these locking mechanisms in .NET Core:

The lock statement: 

The lock statement is a simple way to implement locking in .NET Core. It is used to acquire a lock on an object and execute a block of code while the lock is held. Here is an example of how to use the lock statement to protect access to a shared resource:

private readonly object _lockObject = new object();

private int _sharedResource = 0;

public void AccessSharedResource()

{

    lock (_lockObject)

    {

        // Only one thread at a time can execute this block of code

        _sharedResource++;

    }

}

 

The Monitor class: 

The Monitor class provides a more fine-grained way to implement locking in .NET Core. It allows you to acquire and release locks on objects explicitly, and provides methods for waiting on and signaling other threads. Here is an example of how to use the Monitor class to protect access to a shared resource:

private readonly object _lockObject = new object();

private int _sharedResource = 0;

public void AccessSharedResource()

{

    Monitor.Enter(_lockObject);

    try

    {

        // Only one thread at a time can execute this block of code

        _sharedResource++;

    }

    finally

    {

        Monitor.Exit(_lockObject);

    }

}

 

The ReaderWriterLockSlim class: 

The ReaderWriterLockSlim class is a more advanced locking mechanism in .NET Core. It allows multiple threads to read a shared resource concurrently, but only one thread to write to the resource at a time. Here is an example of how to use the ReaderWriterLockSlim class to protect access to a shared resource:

private readonly ReaderWriterLockSlim _lockObject = new ReaderWriterLockSlim();

private int _sharedResource = 0;

public void AccessSharedResource()

{

    _lockObject.EnterWriteLock();

    try

    {

        // Only one thread at a time can execute this block of code

        _sharedResource++;

    }

    finally

    {

        _lockObject.ExitWriteLock();

    }

}

 

 

Implement Concurrency in SQL Server database and .net core:

In SQL Server, row versioning is a technique for implementing optimistic concurrency control. It works by adding a version column to the table, which stores a unique identifier for each row. When a row is updated, its version identifier is incremented, so that conflicts can be detected during subsequent updates. Here's an example of how to use row versioning with .NET Core:

• Add a version column to the table:

ALTER TABLE dbo.Entities ADD VersionRow TIMESTAMP NOT NULL DEFAULT (GETDATE())

 

• Configure the Entity Framework Core model to include the version column:

public class MyDbContext : DbContext

{

    public DbSet<Entity> Entities { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)

    {

        modelBuilder.Entity<Entity>()

            .Property(e => e.VersionRow)

            .IsRowVersion();

    }

}

 

• Implement optimistic concurrency control in the update method:

// Get the entity to be updated

var entity = await _dbContext.Entities.FindAsync(id);

// Modify the entity's properties

entity.Property1 = newValue1;

entity.Property2 = newValue2;

// Try to save changes, checking for conflicts

try

{

    await _dbContext.SaveChangesAsync();

}

catch (DbUpdateConcurrencyException ex)

{

    var entry = ex.Entries.Single();

    var clientValues = (Entity)entry.Entity;

    var databaseEntry = await entry.GetDatabaseValuesAsync();

    if (databaseEntry == null)

    {

        // The entity has been deleted by another user

    }

    else

    {

        var databaseValues = (Entity)databaseEntry.ToObject();

        // Check for conflicts by comparing version values

        if (databaseValues.VersionRow != clientValues.VersionRow)

        {

            // The entity has been modified by another user

            // Handle the conflict by merging changes or notifying the user

        }

    }

}

In this example, we use the IsRowVersion method to configure the version column in the Entity Framework Core model. Then, in the update method, we use the DbUpdateConcurrencyException class to catch conflicts that occur during save changes. Finally, we compare the version values to detect conflicts and handle them appropriately.

 

It is important to note that handling concurrency and locking can be a complex task, and it is important to thoroughly test and debug your implementation to ensure that it is working correctly.