.NET Developer Interview Questions

Microsoft developed the .NET framework to build and run Windows applications. Originally designed as proprietary software, .NET later became open source, allowing everyone to use it free of charge. Microsoft and the . NET community on GitHub now maintain the wildly popular framework. Because of its versatility — it supports over 60 programming languages, including C# and C++ — .NET developers are in high demand.

Despite the current tech talent shortage, you're likely to be flooded with resumes if you post a job description for a .NET developer. Unfortunately, many of these candidates will be unqualified even for junior-level roles. Although finding qualified developers will still be challenging, asking the right .NET interview questions can help you weed out applicants who don't have the skills you need.

Entry Level .NET Developer Interview Questions

If you're looking for an entry-level developer, your expectations will naturally be lower, but you still want to hire a candidate who has a strong working knowledge of building applications on the .NET framework. To find out if an applicant has a basic understanding of .NET's uses, functions, and capabilities, you can ask the following questions:

What is the .NET framework, and how does it work?

This very basic question will obviously weed out candidates who managed to get through the early screening process without any understanding of .NET. However, don't overlook its potential for evaluating candidates who have advanced technical skills. Developers need to be able to communicate with both tech-savvy people and lay people. A developer who can rattle off the benefits of common language runtime but can't explain how .NET works in simple terms will probably have trouble communicating with non-tech stakeholders.

A good answer to this question will explain that .NET is a framework used to build applications in the Windows environment through an object-oriented approach. It supports various popular languages that are compiled into a Common Intermediate Language (CIL). This compiled code is then stored in an assembly file with a .dll or .exe file extension.

The .NET application uses Common Language Runtime (CLR) to convert the assembly file into machine code via a Just in Time (JIT) compiler. The machine code can then be easily executed by the computer-specific architecture running it.

What are the main components of the .NET framework?

Although they will have touched on the components of .NET in the previous question, this question provides an opportunity for a candidate to show a deeper understanding of the different components and how they work together. Comprehensive answers should include the following information:

Common Language Runtime (CLR)

Common language runtime runs the code and provides valuable services that make developing applications easier regardless of the language used. These services include:

• Garbage collection
• Memory management
• Exception handling
• Type safety
• Thread management
• Security

CLR makes it easier to develop applications whose objects interact across languages since CLR executes all programs written in any supported language.

Common type system

The common type system is an essential part of the CLR's ability to support cross-language integration. It defines how to declare, use, and manage types in CLR. The main functions of the common type system are:

• Establishing a framework for cross-language integration
• Enabling type safety and high-performance execution of code
• Providing an object-oriented model so you can use various programming languages to run applications
• Defining rules that languages must follow to allow objects written in different languages to interact
• Providing a library of primitive data types used for application development

Class libraries

Class libraries are shared libraries in .NET. Their essential function is to allow you to componentize functionalities into modules that can perform in multiple applications. This modularity allows you to reuse components and greatly simplifies the development process. The .NET assembly file format is used to describe class libraries, which fall into one of three types:

• Platform-specific libraries that restrict access to apps and libraries that target that platform but grant access to all APIs on that platform
• Portable-class libraries that can be accessed by apps and libraries that target multiple platforms but only for a subset of APIs
• .NET standard class libraries that combine platform-specific libraries and portable-class libraries into a single model

What is the difference between a value type and a reference type?

Working with types is an important component of developing on the .NET framework, so potential developers should have a solid understanding of both reference and value types.

Value types

Value types contain their data inside their memory location. Value types are usually stored in the stack. Fundamental data types, date, Boolean, structs, and enums are examples of value types. You can copy a value directly by assigning a value type to another variable. You can't derive from a value type, nor can you assign a null value directly to a value type. Instead, you have to use nullable types, which are only a feature in newer versions of .NET.

Reference types

Reference types point to locations in the memory that contain data, and they're stored in the managed heap. When you assign a reference variable to another variable, it creates a copy of the reference instead of copying the value. Reference types consist of classes, objects, arrays, interfaces, and indexes.

Explain the differences between managed and unmanaged code and when you should use each

This question is worth asking because understanding when to use managed code versus unmanaged code is essential. While managed is preferable in most cases, some functions can't be carried out by managed code. A good developer needs to know when to use each for optimal results.

Managed code

The many benefits provided by the Common Language Runtime, such as memory allocation, type safety, and garbage collection, are implemented in the managed runtime environment. With managed code, these services are applied directly to the code without the programmer's input. The .NET framework is necessary for managed code to execute. Managed code has more security features and doesn't depend on the architecture of the machine it runs on.

You should use managed code as often as possible since it's more secure, automatically provides services, and checks for validity and duplication in references. The biggest benefits of using the .NET framework are realized by using managed code.

Unmanaged code

Unmanaged code is any code that the CLR doesn't manage. It doesn't require the .NET framework for execution, and the native runtime environment handles memory management. Unmanaged code has to be recompiled if you want it to run on a different architecture. Unmanaged code requires a more skilled developer since memory allocation, type safety, security, and other services have to be handled by the developer.

You should use unmanaged code only when you need low-level access or direct access to the hardware, or you need to bypass restrictions or parameters in the managed code.

What are the three pillars of object-oriented programming?

Object-oriented programming (OOP) organizes by defining classes and objects. Three pillars underpin OOP: encapsulation, inheritance, and polymorphism.

Encapsulation

Encapsulation bundles data and the methods that operate on it into a single object. Encapsulation is often used to hide the internal state of an object from the outside, which is a process called information hiding. With encapsulation, you can control access to the internal state of an object.

Inheritance

Inheritance is another method of optimizing a developer's work. With inheritance, you can create class hierarchies so that classes and objects can inherit properties and behaviors from their parent. The biggest advantage of inheritance is that you can reuse your previous work without having to start from scratch with each class or object.

Polymorphism

Polymorphism allows one object to have many forms. Using polymorphism, you can perform a single task in different ways. A function or operator can behave differently in different scenarios, depending on the runtime type that invokes it. There are two different types of polymorphism in the .NET framework:

• Compile time or static polymorphism, which is used when creating two or more methods with the same name but different parameters that are decided at the time of compilation
• Runtime polymorphism, which is used when creating same name methods in inherited class and what will override the functionality of base class

What base class gives all web forms their inheritance?

Developers should understand that all web forms inherit features from the page class.

Intermediate-level .NET Developer Interview Questions

A .NET developer with over three years of experience should be able to easily answer all of the above questions in detail and should know more advanced concepts as well. A mid-level developer will be expected to handle significant portions of projects without supervision. They should be able to work seamlessly as part of a team and deliver high-quality code. Additionally, mid-level developers will be expected to serve as mentors to more junior-level colleagues. You should place a high priority on soft skills such as communication and collaboration for mid-level developers. Here are some questions you can ask to gauge a mid-level .NET developer's expertise:

What are the parts of the assembly?

An assembly can be created from one or more source code files. They allow you to break up larger projects so that multiple developers can work on different modules that can be assembled into a single unit. Assemblies can be either .exe or DLL files. An assembly is comprised of four sections;

• The manifest contains information about the assembly version
• The type metadata contains the binary code of the program
• Microsoft Intermediate Language Code
• The resources are lists of related files

What are the types of assemblies?

There are two types of assemblies:

Private assemblies

Private assemblies are accessible only to the application. A private assembly can only be accessed by copying. You must copy a private assembly separately into every application folder where you want to use it. Private assemblies must be installed in the application's installation directory.

Public or shared assemblies

Multiple applications can use public assemblies. You only need one copy of a public assembly at the system level to share among multiple applications. Public assemblies are installed in the General Assembly Cache (GAC).

Explain the differences between MDI and SDI

An MDI is a multiple-document interface, and an SDI is a single-document interface. An MDI allows you to open multiple document windows using one parent window and multiple child windows. The components of the parent window are shared with the child windows.

An SDI opens each document in a separate window with its own components, such as menus, toolbars, etc. An SDI isn't constrained by the parent window.

What does the garbage collector in .NET do?

Garbage collecting is the process of maintaining memory aspects to prevent memory leaks during execution. The garbage collector allocates and reallocates memory as required by an application. It does this by checking the references of the variables and objects used by the application. When an application no longer requires an object, its memory is deallocated and freed up.

What are the three generations of garbage collection?

Garbage collecting goes through three generations in .NET including:

• Generation 0, which stores short-lived objects
• Generation 1, which stores objects moved from Generation 0
• Generation 2, which stores long-lived objects and objects moved from Generation 1

What is caching?

Caching stores data temporarily in the memory for easier access compared to searching for it in its original location. Caching increases the speed and efficiency of an application. The three types of caching are:

• Page caching
• Data caching
• Fragment caching

Explain CAS and what type of code it can be used with

CAS stands for code access security. It's part of a security model designed to prevent unauthorized access to resources. CLR executes the code based on the permissions. CAS can only be used on managed code. Assemblies that use CAS are treated as partially trusted, although it still has to go through checks each time it attempts to access the resources.  

What are globalization and localization?

Globalization is developing applications to support many languages, while localization changes a global application to serve a specific language or culture. Microsoft.Extensions.Localization is used to localize content. Existing applications can be converted via globalization to support multiple languages.

What is Model View Controller?

Model View Controller (MVC) is a type of architecture used to build .NET applications. There are three logical components to Model View Controller:

Model

The model holds data and related logic. It handles object storage and retrieval from databases.

View

View handles the UI aspects of an application. Models give information to views for display.

Controller

The controller takes the user input and renders the final output.

What are the differences between constants and read-only variables, and when should you use each?

Read-only variables are evaluated at run time, while constants are evaluated at compile time. Read-only variables can hold reference-type variables. Constants support value-type variables and strings. Read-only variables can only be initiated in a constructor or at the time of declaration.

You should use read-only variables when their actual value is unknown before run time. You should use constants when the value is not changing during run time.

What are the events in the page lifecycle?

When a page is requested, it's loaded into the server memory, processed, and sent to the browser. The phases of the page lifecycle include:

• Initialization
• Controls on the page are instantiated
• The page state is restored and maintained
• Event handler codes are executed
• Page is rendered

What is role-based security?

Role-based security implements security based on the users' roles. Users can be assigned roles in their organizations, such as user, administrator, and guest, and authorization is granted based on the role.

Give some examples of design patterns used in .NET?

There are numerous design patterns used in .NET. A developer should understand many different design patterns and when to use them. Choosing the right design pattern is essential to creating code that's easy to scale and maintain. Some common design patterns include:

Singleton

This pattern ensures that a class has only one instance and provides a global access point.

Factory

This pattern provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created.

Observer

This pattern defines a one-to-many dependency between objects so all dependents are notified and updated automatically when one object changes state.

Builder

This pattern separates the construction of a complex object from its representation, allowing the same construction process to create various representations.

Prototype

This pattern allows objects to be created by copying pre-existing objects instead of creating new objects from scratch.

Adapter

This pattern allows two incompatible classes to work together by converting the interface of one class into an interface expected by the other class.

Decorator

This pattern allows new functionality to be dynamically added to an existing object without modifying its interface.

Senior .NET Developer Interview Questions

Senior .NET developers have more responsibility and can lead a team of developers. Some of the responsibilities of a senior .NET developer include:

• Analyzing business requirements from stakeholders and translating them into technical solutions
• Designing and developing scalable, maintainable software applications
• Collaborating with cross-functional teams to develop and implement software solutions
• Mentoring and guiding junior developers
• Leading the development of technical solutions and ensuring that the team follows best practices and coding standards
• Participating in code reviews to ensure code quality and adherence to standards
• Troubleshooting and debugging complex issues in the software

Of course, you want a senior-level developer to have advanced technical skills, but once you've established their expertise, you should focus on leadership skills. Here are some questions that will help you evaluate the leadership potential of senior-level candidates:

Can you describe a challenging project you worked on and how you led your team to success?

This question will allow an applicant to explain what they've worked on and their leadership style. You should listen closely to their answer to understand how they approach problem-solving and determine if how they lead is compatible with your teams.

How do you prioritize tasks and manage your team's workload to meet project deadlines?

Project management is an essential part of a senior .NET developer's duties. This question will give you insight into how a candidate plans and manages projects effectively. Look for answers that include:

• Using project management tools to create a list of tasks, assign them to team members, and track their progress
• Creating a task list to break down the project into smaller, manageable tasks that can be prioritized
• Identifying the tasks that will have the biggest impact on the project and focusing on those first
• Regularly communicating with the team to get ahead of obstacles before they get out of hand
• Checking in with team members to ensure they're not overwhelmed with their workload

Hiring NET Developers

There are many hurdles to overcome when trying to find a qualified .NET developer. The competition is fierce in today's competitive labor market. Talented .NET developers have specialized skills that command a high salary, but you'll be flooded with a large pool of unqualified applicants when you post a job ad. Even when you screen for technical skills, you've just begun the process. Hiring a .NET developer is not just about technical skills; finding someone who will be a good fit for your organization's culture and work environment is also important.

The search for a skilled developer can consume a lot of your company's resources. Working with a talent development partner like Revelo can save you time and money by providing you with a pool of skilled, pre-vetted developers. Our Latin American developers are proficient in English and talented in all the most in-demand tech stacks.

At Revelo, we help you source, hire, and pay world-class engineering talent. Our end-to-end talent solution provides remote tech talent in US-aligned time zones. You can build and scale your software development teams without the hassles of foreign payroll and compliance issues. We handle the administrative HR tasks so you can focus on growing your business. Reach out to find your ideal developers.