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Landing a developer role in the C# .NET domain can be quite challenging, especially with the ever-changing landscape of technology. To help you prepare for your next interview, we’ve compiled a list of 30 essential C# .NET interview questions and answers. Use this guide to brush up on your knowledge and ace that interview!
Q1: What are the differences between .NET Core and .NET Framework?
.NET Core is an open-source, cross-platform framework developed by Microsoft. It’s lightweight, modular, and optimized for high-performance, cloud-based applications. On the other hand, the .NET Framework is a Windows-only framework, designed primarily for creating Windows applications.
Q2: What are the benefits of using Dependency Injection (DI) in a C# .NET application?
Dependency Injection (DI) improves maintainability, testability, and flexibility of an application by promoting loose coupling, separation of concerns, and inversion of control. It makes it easier to swap out or mock dependencies during testing.
Q3: What is the difference between IEnumerable, ICollection, and IList interfaces in C#?
IEnumerable is a basic interface allowing traversal of a collection using a foreach loop. ICollection extends IEnumerable, adding methods for modifying collections like Add, Remove, and Clear, and properties like Count and IsReadOnly. IList further extends ICollection, providing methods for accessing elements by index and inserting or removing elements at specific positions.
Q4: Explain the concept of delegates in C#.
A delegate is a type-safe function pointer in C# that holds a reference to a method with a specific signature. It enables you to pass methods as parameters, create event handlers, and define callback functions.
Q5: What is the difference between an abstract class and an interface in C#?
An abstract class is a class that cannot be instantiated and can contain both abstract (without implementation) and non-abstract methods. An interface, on the other hand, is a contract that only contains method signatures without any implementation. A class can inherit from multiple interfaces but only one abstract class.
Q6: What are async and await keywords in C#?
Async and await are keywords in C# used for writing asynchronous code. The async keyword is used to mark a method as asynchronous, while the await keyword is used to pause the execution of the method until the awaited task is completed, allowing other operations to continue.
Q7: How does the ‘using’ statement work in C#?
The ‘using’ statement in C# is used to ensure that an object implementing the IDisposable interface is properly disposed of after its usage. It simplifies the code by automatically calling the Dispose method at the end of the block, reducing the risk of resource leaks.
Q8: Explain the difference between var, dynamic, and object in C#.
Var is a keyword used for implicitly typed variables, where the type is determined at compile-time based on the assigned value. Dynamic allows for runtime type binding, enabling the type to be determined at runtime. Object is the base class for all types in C#, and a variable declared as an object can hold any type, but requires casting for specific operations.
Q9: What is LINQ, and how is it used in C#?
LINQ (Language Integrated Query) is a set of features in C# that allows querying data from different sources (such as collections, databases, or XML) using a consistent and expressive syntax. It enables you to write more readable and concise code for data manipulation and retrieval.
Q10: What is the difference between String and StringBuilder in C#?
String is an immutable class in C#, meaning that any modification creates a new instance, which can lead to performance issues in scenarios involving numerous concatenations. StringBuilder, on the other hand, is a mutable class designed for efficient string manipulation, minimizing the overhead of creating new instances.
Q11: What are attributes in C#?
Attributes are a way to associate metadata with code elements (such as classes, methods, properties, or fields) in C#. They are used for various purposes like providing additional information, controlling behavior, or specifying relationships between elements.
Q12: Explain the concept of exception handling in C#.
Exception handling in C# is a mechanism to detect and handle runtime errors. It uses the keywords try, catch, and finally to define blocks of code that handle exceptions, allowing you to recover gracefully from errors and maintain the flow of your application.
Q13: What are extension methods in C#?
Extension methods are a way to add new methods to existing types without modifying their source code or creating derived types. They are static methods defined in a static class and called as if they were instance methods of the extended type.
Q14: How can you implement thread synchronization in C#?
Thread synchronization in C# can be achieved using various constructs, such as lock, Mutex, Semaphore, and Monitor. These constructs help in coordinating the execution of multiple threads, ensuring that only one thread can access a shared resource or critical section at a time, preventing race conditions and data corruption.
Q15: Explain the difference between Task and Thread in C#.
A Thread is a low-level representation of an independent execution path in an application, while a Task is a high-level abstraction built on top of threads. Tasks provide better performance and scalability by leveraging the ThreadPool, making it easier to write asynchronous and parallel code in C#.
Q16: What is the purpose of the ‘yield’ keyword in C#?
The ‘yield’ keyword is used in iterator methods to create a stateful, custom iterator that can be used with a foreach loop. It enables you to return a sequence of values, one at a time, on-demand, improving performance and memory usage for large data sets.
Q17: What is the difference between ref and out keywords in C#?
Both ref and out keywords are used to pass arguments by reference, allowing a method to modify the original value of the argument. The difference is that ref requires the argument to be initialized before it is passed to the method, while out does not, but it must be assigned within the method before it returns.
Q18: Explain the concept of garbage collection in CSharp
Garbage collection in C# is an automatic memory management mechanism that deallocates memory occupied by unreachable objects. The .NET runtime periodically checks for objects without any references and frees the memory, reducing the risk of memory leaks and improving application performance.
Q19: What are the key features of C# 9?
C# 9 introduces several features, including:
- Record types: Immutable reference types with value semantics.
- Init-only properties: Properties that can only be set during object initialization.
- Top-level statements: Simplified program structure without the need for a Main method.
- Pattern matching enhancements: More expressive patterns and improved switch statements.
- Target-typed new expressions: Simplified object creation with inferred types.
Q20: How do you implement a singleton pattern in C#?
A singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It can be implemented in C# using a combination of a private constructor, a static readonly instance field, and a public static property or method to access the instance.
Q21: What is the purpose of the ‘sealed’ keyword in C#?
The ‘sealed’ keyword is used to prevent further inheritance of a class or override of a method. Sealed classes cannot be used as base classes, and sealed methods in a derived class cannot be overridden by further derived classes.
Q22: Explain the concept of anonymous functions in CSharp
Anonymous functions are inline, unnamed functions used as arguments for other functions or as delegates. They are a convenient way to define small, single-use functions without the need for a separate named method. In C#, anonymous functions can be defined using lambda expressions or anonymous methods.
Q23: What is the Global Assembly Cache (GAC) in .NET?
The Global Assembly Cache (GAC) is a central repository for shared .NET assemblies on a machine. It allows multiple applications to share the same assembly, reducing disk space and avoiding versioning conflicts through side-by-side deployment of different assembly versions.
Q24: How do you create and use a custom attribute in C#?
To create a custom attribute, define a new class that inherits from the System.Attribute class and apply the AttributeUsageAttribute to specify its usage. To use a custom attribute, apply it to the target code element using square brackets, and optionally provide values for its properties or constructor parameters. To read custom attributes at runtime, use reflection to obtain information about the target element and retrieve the attributes using the GetCustomAttributes method.
Q25: What are the main differences between WPF and WinForms?
WPF (Windows Presentation Foundation) is a modern UI framework for creating Windows applications, offering advanced graphics capabilities, rich styling, and data binding support. WinForms, on the other hand, is an older framework that uses standard Windows controls and has limited styling and graphics capabilities. WPF is generally more flexible and powerful, while WinForms is simpler and has better designer support in Visual Studio.
Q26: What is Entity Framework, and how does it work?
Entity Framework is an Object-Relational Mapping (ORM) framework for .NET that simplifies data access by allowing developers to work with objects and properties instead of tables and columns. It translates LINQ queries into SQL commands, handles database connections, and maps query results back to objects, providing a higher level of abstraction and reducing boilerplate code.
Q27: What is the difference between early binding and late binding in C#?
Early binding refers to resolving the types, methods, and properties at compile-time, providing better performance and type safety. Late binding, on the other hand, resolves these elements at runtime using reflection, allowing more flexibility but with increased complexity and reduced performance.
Q28: What is the purpose of the ‘volatile’ keyword in C#?
The ‘volatile’ keyword is used to indicate that a field can be accessed by multiple threads and that its value can change unexpectedly. It ensures that the most up-to-date value is always read from the memory, preventing compiler optimizations that could lead to incorrect results in multi-threaded scenarios.
Q29: What is the difference between ‘==’ and ‘Equals’ in C#?
The ‘==’ operator is used to compare the reference equality of two objects, checking whether they point to the same instance in memory. The ‘Equals’ method, on the other hand, checks for value equality, determining whether two objects have the same content or state. For value types, the ‘==’ operator and ‘Equals’ method behave the same, but for reference types, their behavior can differ.
Q30: How do you implement and consume a RESTful API in C#?
To implement a RESTful API in C#, you can use ASP.NET Core Web API, which supports creating, hosting, and consuming RESTful services. Use attributes like [HttpGet], [HttpPost], [HttpPut], and [HttpDelete] to define the HTTP verbs for your API methods. To consume a RESTful API, you can use the HttpClient class, which provides methods for sending HTTP requests and receiving HTTP responses, enabling you to interact with the API programmatically.
By reviewing these 30 C# .NET interview questions and answers, you should be well-prepared for your interview. Remember to brush up on the fundamentals, understand the advanced concepts, and stay updated with the latest features and trends. Good luck!
FAQs
- What is the main advantage of using .NET Core over .NET Framework? .NET Core is cross-platform, open-source, and optimized for high-performance, cloud-based applications, while .NET Framework is primarily for creating Windows applications.
- What are the main benefits of using Dependency Injection in C#? Dependency Injection improves maintainability, testability, and flexibility by promoting loose coupling, separation of concerns, and inversion of control.
- How does garbage collection work in C#? Garbage collection in C# is an automatic memory management mechanism that deallocates memory occupied by unreachable objects, periodically checking for objects without any references and freeing the memory, reducing the risk of memory leaks and improving application performance.
- What is the main difference between IQueryable and IEnumerable in C#? IQueryable extends IEnumerable and is optimized for querying data from external sources like databases, enabling deferred execution and generating efficient SQL queries. IEnumerable is more suitable for in-memory collections and does not support deferred execution.
- What are some best practices for writing clean, maintainable C# code? Some best practices include following the SOLID principles, using meaningful names, writing small and focused methods, providing proper comments and documentation, adhering to the DRY (Don’t Repeat Yourself) principle, and consistently following a coding standard or style guide.
Here are a few more articles of mine I would suggest to read on C# .NET to improve your base knowledge:
Thank you for reading :)