47 .NET Core interview questions and answers to hire top developers

As a recruiter or hiring manager, identifying the right .NET Core developer can be challenging. Having a list of well-thought-out interview questions is key to evaluating candidates effectively during the recruitment process.

This blog post provides various .NET Core interview questions tailored to different experience levels and focuses, from general to technical definitions. It covers questions to ask junior, mid-tier developers, and those related to processes and tasks.

Using this list can streamline your interview process and help you identify top talent more efficiently. For a more thorough assessment, consider using an Adaface .NET test before the interview.

Table of contents

8 general .NET Core interview questions and answers

Whether you're gearing up for your next round of interviews or just want to ensure your candidates know their stuff, this list of .NET Core interview questions will help you determine the depth of their knowledge. Perfect for keeping your interviews both sharp and insightful, these questions cover essential topics every .NET Core developer should be familiar with.

1. What are the main benefits of using .NET Core compared to the .NET Framework?

.NET Core offers several benefits over the traditional .NET Framework, including cross-platform support, meaning it can run on Windows, macOS, and Linux. This flexibility allows developers to create applications that can run on multiple operating systems without needing significant code changes.

Additionally, .NET Core is open source, which means it has a large community contributing to its development and improvement. It also provides better performance and scalability, making it suitable for modern cloud-based applications.

Look for a candidate who emphasizes these points and demonstrates an understanding of how these benefits can impact project development and deployment.

2. Can you explain what dependency injection is and why it is useful in .NET Core?

Dependency injection is a design pattern used to implement Inversion of Control. It allows the creation of dependent objects outside of a class and provides those objects to a class through different ways, typically via constructor injection.

In .NET Core, dependency injection is built-in, which helps in managing services and their lifetimes. It makes the code more modular, testable, and easier to maintain by decoupling the creation of an object from its usage.

An ideal answer should include an explanation of how dependency injection helps in creating more maintainable and testable code structures.

3. How does .NET Core handle memory management?

.NET Core handles memory management through a process called garbage collection. This automated system manages the allocation and release of memory for your application, preventing memory leaks and ensuring that unused objects are removed from memory.

Garbage collection in .NET Core is efficient and works in the background, allowing developers to focus on writing code without worrying excessively about memory management.

Candidates should demonstrate an understanding of garbage collection and its benefits in simplifying memory management in .NET Core applications.

4. What is Kestrel, and why is it used in .NET Core?

Kestrel is a cross-platform web server that is included with ASP.NET Core. It is designed to handle both static and dynamic content, making it a versatile choice for .NET Core web applications.

Kestrel is known for its lightweight and high-performance characteristics, which make it suitable for serving HTTP requests directly or being used as an edge server in a reverse proxy setup.

Look for candidates who understand Kestrel’s role in enhancing the performance and scalability of ASP.NET Core applications.

5. Can you explain what middleware is in .NET Core and its role in request processing?

Middleware in .NET Core is software that's assembled into an application pipeline to handle requests and responses. Each middleware component chooses whether to pass the request to the next component in the pipeline and can perform operations before and after the next component is invoked.

Middleware components can be used for various purposes such as authentication, logging, and error handling. They provide a convenient way to add cross-cutting concerns to your application.

An ideal candidate will highlight the modular nature of middleware and describe how it simplifies the addition of common functionalities across different parts of the application.

6. What is the role of the Startup class in a .NET Core application?

The Startup class in a .NET Core application is responsible for configuring the services and the app's request pipeline. It typically contains two methods: ConfigureServices and Configure.

ConfigureServices is used to add services to the dependency injection container, while Configure is used to set up the middleware pipeline that handles requests.

Candidates should explain how the Startup class is crucial in initializing and configuring the application, ensuring all necessary services and middleware are properly set up.

7. What are some common uses for configuration files in .NET Core?

Configuration files in .NET Core, such as appsettings.json, are commonly used to store settings and configurations that an application requires, such as connection strings, API keys, and other environment-specific settings.

These files allow for a more flexible and maintainable approach to managing configurations, as they can be easily changed without modifying the codebase. They support multiple environments by allowing different configuration files for each environment.

Candidates should demonstrate an understanding of the importance of configuration files for maintaining clean code and ease of updates.

8. How do you handle exceptions in .NET Core?

In .NET Core, exceptions can be handled using try-catch blocks, custom middleware, or global exception handling. The ExceptionHandlerMiddleware is commonly used to catch and process exceptions across the entire application.

Developers can also use the UseExceptionHandler method in the middleware pipeline to handle exceptions and provide custom error responses to users.

An ideal candidate should explain the importance of exception handling in providing a good user experience and maintaining application stability.

10 .NET Core interview questions to ask junior developers

To effectively assess the foundational knowledge and practical skills of junior developers in .NET Core, consider using these targeted questions during your interviews. This list can guide you in evaluating their understanding of essential concepts and their ability to apply them in real-world scenarios, making it a valuable addition to your recruitment process. For more insights, check out our job descriptions.

1. What is the difference between a .NET Core application and a .NET Framework application in terms of cross-platform compatibility?
2. Can you explain the purpose of the appsettings.json file in a .NET Core project?
3. How do you set up dependency injection in .NET Core applications?
4. What is the significance of the 'ConfigureServices' method in the Startup class?
5. Can you describe the concept of routing in ASP.NET Core?
6. What are Razor Pages, and how do they differ from MVC in .NET Core?
7. How does .NET Core support logging, and what are some common logging providers you can use?
8. What is the purpose of Entity Framework Core in .NET applications, and how does it differ from traditional ADO.NET?
9. Can you explain what a NuGet package is and how to manage them in a .NET Core project?
10. What is the role of the 'LaunchSettings.json' file in a .NET Core application?

10 intermediate .NET Core interview questions and answers to ask mid-tier developers

To determine whether your mid-tier developers have a solid understanding of .NET Core, ask them some of these 10 intermediate .NET Core interview questions. This list will help you gauge their practical knowledge and problem-solving skills, ensuring they can handle more complex tasks than junior developers.

1. Can you explain the role of the 'ServiceProvider' in .NET Core dependency injection?

The 'ServiceProvider' in .NET Core is responsible for managing the lifecycle of the services that are registered in the dependency injection container. When a service is requested, the 'ServiceProvider' resolves it and handles its dependencies.

An ideal candidate should mention that the 'ServiceProvider' is usually built during the application startup and is used throughout the application to resolve service instances. They should also highlight the importance of proper service lifetime management to avoid memory leaks and ensure optimal performance.

2. What is the significance of the 'Configure' method in the Startup class?

The 'Configure' method in the Startup class is used to set up the application's request processing pipeline. This is where middleware components are added to handle requests and responses.

Candidates should point out that the order in which middleware is added is crucial, as it determines the flow of request processing. Look for responses that demonstrate an understanding of how to configure and order middleware effectively.

3. How does .NET Core handle cross-platform development?

.NET Core is designed to be a cross-platform framework, meaning it can run on Windows, macOS, and Linux. This is achieved through a modular architecture and the use of platform-agnostic code.

A good answer will highlight that .NET Core uses runtime environments and libraries that are platform-independent. Candidates should also mention the importance of testing applications on all target platforms to ensure compatibility.

4. What are the different types of service lifetimes in .NET Core?

In .NET Core, services can have three types of lifetimes: Singleton, Scoped, and Transient. Singleton services have a single instance throughout the application's lifetime. Scoped services are created once per request. Transient services are created each time they are requested.

Look for candidates who can explain when to use each service lifetime. For example, Singleton is suitable for stateful services, while Transient is better for lightweight, stateless services.

5. Can you explain what 'self-contained deployment' means in .NET Core?

'Self-contained deployment' in .NET Core means packaging the application with the .NET Core runtime and all its dependencies. This allows the application to run on a machine without needing a pre-installed .NET Core runtime.

Candidates should understand that this type of deployment can be useful for scenarios where you can't guarantee the target environment has the .NET Core runtime installed. However, it results in a larger package size compared to 'framework-dependent deployment'.

6. How do you implement logging in a .NET Core application?

Logging in .NET Core is implemented through the built-in logging framework, which can be configured in the application's Startup class. You can log messages at various levels (e.g., Information, Warning, Error) and use different logging providers like Console, Debug, and third-party services.

An ideal candidate would explain the importance of logging for monitoring and debugging applications. They should also be able to discuss configuring log levels and setting up different logging providers effectively.

7. What is 'Health Checks' in .NET Core, and how do you set it up?

Health Checks in .NET Core are used to monitor the health and status of an application. This includes checking the status of databases, external services, and other dependencies.

Candidates should describe how to set up Health Checks by adding the appropriate services in the ConfigureServices method and then configuring the endpoint in the Configure method of the Startup class. Look for answers that emphasize the importance of real-time monitoring for maintaining application reliability.

8. Can you explain the purpose of 'Hosting Environment' in .NET Core?

The 'Hosting Environment' in .NET Core provides information about the web hosting environment an application is running in. It allows developers to configure settings and services based on the environment (e.g., Development, Staging, Production).

A good answer should include how to access and use the 'IHostingEnvironment' interface to make decisions based on the current environment. This is crucial for configuring things like logging levels or connection strings differently for each environment.

9. What are 'Tag Helpers' in ASP.NET Core, and how do they enhance development?

'Tag Helpers' in ASP.NET Core are components that enable server-side code to participate in creating and rendering HTML elements in Razor views. They provide an HTML-friendly development experience by binding server-side logic with the HTML markup.

Candidates should explain that Tag Helpers improve readability and maintainability of code by keeping the markup clean and semantic. Look for examples of common Tag Helpers like form and input helpers, and how they simplify HTML generation.

10. How do you handle configuration settings in a .NET Core application?

Configuration settings in .NET Core are typically handled through various configuration providers such as JSON files (e.g., appsettings.json), environment variables, and command-line arguments. These can be accessed through the IConfiguration interface.

An ideal candidate should discuss how to set up and access these configurations in the Startup class. They should also mention the importance of secure handling of sensitive information, potentially using services like Azure Key Vault.

10 .NET Core interview questions about processes and tasks

To assess a candidate's understanding of processes and tasks in .NET Core, use these targeted questions during the interview. They will help you gauge the applicant's practical knowledge and readiness for real-world challenges in .NET development. For more insight on candidate expectations, you can explore the job descriptions.

1. Can you explain the process of creating and managing background tasks in .NET Core?
2. How do you implement asynchronous programming in .NET Core, and what are its benefits?
3. What is the role of the Task Parallel Library (TPL) in .NET Core applications?
4. Can you describe how to use the IHostedService interface for background services in .NET Core?
5. What approaches can you take for handling long-running tasks in a .NET Core application?
6. How do you manage cancellation tokens in .NET Core, and why are they important?
7. Can you explain the concept of task scheduling in .NET Core?
8. How do you handle thread safety when working with shared resources in .NET Core?
9. What are the differences between async/await and traditional threading in .NET Core?
10. How can you implement a retry mechanism for failed tasks in a .NET Core application?

9 .NET Core interview questions and answers related to technical definitions

To gauge whether your .NET Core candidates have a solid grasp of technical concepts, use these questions to dive into definitions and core principles. These questions will help you assess a candidate's theoretical knowledge, which is crucial for any .NET developer role. Remember, the goal is to understand their depth of knowledge, not just their ability to recite memorized facts.

1. Can you explain what 'Just-In-Time' compilation means in the context of .NET Core?

Just-In-Time (JIT) compilation in .NET Core is a process where intermediate language (IL) code is converted into native machine code at runtime, just before execution. This approach offers several advantages:

• Improved performance as the code is optimized for the specific hardware it's running on
• Smaller initial download size for applications
• The ability to make runtime optimizations based on actual usage patterns

Look for candidates who can explain the concept clearly and discuss its benefits. Strong candidates might also mention how JIT compilation contributes to the cross-platform capabilities of .NET Core.

2. What is the Common Language Runtime (CLR) in .NET Core and what role does it play?

The Common Language Runtime (CLR) is the virtual machine component of .NET Core that manages the execution of .NET programs. It provides important services such as:

• Memory management and garbage collection
• Type safety and exception handling
• Security management
• Thread management

A good answer should highlight how the CLR abstracts the details of the underlying platform, allowing developers to focus on writing code rather than managing system-level details. Look for candidates who can explain how the CLR contributes to the language interoperability feature of .NET Core.

3. Can you describe what 'boxing' and 'unboxing' mean in .NET Core?

Boxing is the process of converting a value type to the type object or any interface type implemented by this value type. Unboxing extracts the value type from the object. In other words:

• Boxing is wrapping a value type in an object
• Unboxing is extracting the value type from an object

Look for candidates who can explain these concepts clearly and discuss their performance implications. Strong candidates might mention that while boxing and unboxing provide flexibility, they can impact performance if overused, and might suggest alternatives like generics for better type safety and performance.

4. What is the Global Assembly Cache (GAC) and how is it different in .NET Core compared to .NET Framework?

The Global Assembly Cache (GAC) is a machine-wide cache for .NET assemblies. In the .NET Framework, it was used to store and share assemblies that were intended to be used by multiple applications on the computer.

In .NET Core, the concept of GAC doesn't exist. Instead, .NET Core uses a side-by-side versioning approach where each application can have its own version of the framework and libraries.

Look for candidates who can explain this shift in approach and discuss its benefits, such as easier deployment and reduced chances of DLL conflicts. Strong candidates might also touch on how this change aligns with .NET Core's goals of being more modular and cross-platform friendly.

5. What is the purpose of the 'IDisposable' interface in .NET Core?

The IDisposable interface in .NET Core provides a mechanism for releasing unmanaged resources. Classes that implement IDisposable have a Dispose() method that should be called when the object is no longer needed.

Common uses include:

• Closing file handles
• Releasing database connections
• Freeing up any other unmanaged resources

Look for candidates who understand the importance of proper resource management. Strong candidates might discuss the 'using' statement as a clean way to ensure Dispose() is called, or mention the connection between IDisposable and the garbage collector's finalization process.

6. Can you explain what a 'delegate' is in .NET Core and provide an example of when you might use one?

A delegate in .NET Core is a type that represents references to methods with a particular parameter list and return type. Essentially, delegates are function pointers that allow methods to be passed as parameters.

Common use cases for delegates include:

• Event handling
• Callback methods
• Implementing the observer pattern

Look for candidates who can clearly explain the concept and provide practical examples. Strong candidates might discuss how delegates relate to lambda expressions or how they're used in LINQ. They might also mention multicast delegates for invoking multiple methods with a single call.

7. What is the difference between 'ref' and 'out' parameters in .NET Core?

Both 'ref' and 'out' keywords in .NET Core are used to pass arguments by reference, but they have some key differences:

• 'ref' requires the variable to be initialized before passing it to the method
• 'out' doesn't require initialization, but the method must assign a value before the method returns
• 'ref' can pass values both into and out of a method, while 'out' is only for passing values out

Look for candidates who can clearly articulate these differences. Strong candidates might discuss scenarios where each would be appropriate, or mention performance considerations when using ref and out parameters.

8. Can you explain what 'reflection' means in .NET Core and provide an example of when it might be useful?

Reflection in .NET Core is the ability of a program to examine, introspect, and modify its own structure and behavior at runtime. It allows for dynamic creation of types, binding types to existing objects, or getting the type from an existing object and invoking its methods or accessing its fields and properties.

Common use cases for reflection include:

• Creating instances of types dynamically
• Accessing private members for unit testing
• Implementing plugin architectures
• Serialization and deserialization

Look for candidates who can explain the concept clearly and provide practical examples. Strong candidates might discuss the performance implications of using reflection or mention how it relates to attributes and dependency injection in .NET Core.

9. What is the difference between 'const' and 'readonly' in .NET Core?

Both 'const' and 'readonly' in .NET Core are used to create values that cannot be modified, but they have some key differences:

• 'const' values are compiled into the assembly and must be known at compile-time
• 'readonly' values can be set at runtime in the constructor
• 'const' is implicitly static, while 'readonly' can be instance-level
• 'const' can only be used with primitive types and strings, while 'readonly' can be used with any type

Look for candidates who can clearly articulate these differences. Strong candidates might discuss scenarios where each would be appropriate, or mention how these keywords relate to immutability and thread safety in .NET Core applications.

Which .NET Core skills should you evaluate during the interview phase?

Evaluating a candidate's abilities in a single interview can be challenging. However, for .NET Core roles, there are specific skills that are essential for hiring managers to focus on. These skills play a significant role in determining a candidate's capability to thrive in a .NET Core environment.

C# Proficiency

To assess a candidate's C# skills, consider using an assessment test that includes relevant multiple-choice questions. Tests like the C# online test can help filter candidates effectively.

In addition to tests, targeted interview questions can provide insight into a candidate's understanding of C#. One such question to consider is:

Can you explain the differences between an abstract class and an interface in C#?

When asking this question, look for clarity in their explanation. A strong candidate should be able to articulate how abstract classes allow for code reuse while interfaces promote flexibility and multiple inheritances.

ASP.NET Core Framework

Utilizing an assessment test with multiple-choice questions related to ASP.NET Core can help gauge a candidate's familiarity with the framework. The ASP.NET online test is a useful resource to filter candidates.

To further assess their knowledge, you could ask the following question:

What is middleware in ASP.NET Core and how is it used?

Listen for a comprehensive answer that includes the definition of middleware and examples of common middleware components. Candidates should demonstrate an understanding of how middleware components are used to handle requests and responses.

Entity Framework Core

To evaluate candidate skills in this area, consider using an assessment that includes relevant MCQs. You could look into an Entity Framework online test for effective filtering.

Additionally, you may want to ask candidates the following question:

What are the advantages of using Entity Framework Core over traditional ADO.NET?

When posing this question, focus on their ability to explain the benefits such as reduced boilerplate code and better integration with LINQ, which makes querying data more intuitive.

Maximizing Your .NET Core Interview Process: Key Tips

Before putting your newfound knowledge to use, consider these tips to enhance your .NET Core interview process. These strategies will help you make the most of your candidate evaluations.

1. Implement Skills Tests for Initial Screening

Skills tests can significantly streamline your hiring process by objectively evaluating candidates' technical abilities before the interview stage. This approach saves time and ensures you're focusing on the most qualified applicants.

For .NET Core positions, consider using tests that cover C#, ASP.NET, and SQL Server. Adaface offers a .NET Online Test and a C# .NET Test that can help assess these skills comprehensively.

By incorporating these tests, you can quickly identify candidates with strong technical foundations. This allows you to focus your interviews on more nuanced aspects of their experience and problem-solving abilities.

2. Curate a Balanced Set of Interview Questions

With limited interview time, it's crucial to select a mix of questions that cover various aspects of .NET Core development. This approach ensures a well-rounded evaluation of the candidate's skills and experience.

Consider including questions about related technologies like Entity Framework or Azure. These can provide insights into the candidate's broader technical knowledge.

Don't forget to assess soft skills such as communication and problem-solving. These are equally important for a developer's success in a team environment.

3. Master the Art of Follow-Up Questions

Asking effective follow-up questions is key to understanding a candidate's true depth of knowledge. It helps distinguish between those who have memorized answers and those with genuine understanding and problem-solving skills.

For example, after asking about dependency injection in .NET Core, follow up with a question about how they've implemented it in a recent project. This approach reveals practical experience and decision-making processes, giving you a clearer picture of the candidate's capabilities.

Leveraging .NET Core Interview Questions and Skill Tests for Effective Hiring

When hiring for roles requiring specific .NET Core skills, it’s important to verify candidate capabilities accurately. The most straightforward way to assess these skills is through targeted skill tests. Consider using assessments like the .NET Online Test or the C# .NET Test to reliably measure applicant aptitude in .NET Core.

After administering these tests, you can efficiently shortlist the top candidates for further interviews. To streamline this process, sign up on our platform through this link and explore various testing options that suit your hiring needs.

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