Best Kotlin Interview Questions To Ask A Developer

As Kotlin continues to gain popularity in the realm of Android app development, the need for skilled Kotlin developers has never been greater.

To help you assess a candidate's knowledge and expertise in Kotlin, we have compiled a comprehensive list of the best Kotlin interview questions.

1. Explain the differences between val and var in Kotlin.

An understanding of val and var provides insight into a candidate's knowledge of basic Kotlin syntax and principles. Mutable (var) and immutable (val) declarations are integral to the language.

You can also gauge the candidate's awareness of coding practices around immutability and data consistency, which are crucial for maintaining reliable and error-free code.

2. What is a data class in Kotlin? Can you give an example?

A solid understanding of data classes in Kotlin is crucial as it can significantly reduce boilerplate code, enhancing code readability and maintainability.

This question can provide insight into a candidate's practical use of these classes, and their proficiency in the language's features designed to streamline coding efforts.

3. How does null safety work in Kotlin?

Kotlin's null safety feature is key to preventing null pointer exceptions, a common source of application crashes.

A clear understanding of this feature shows a candidate's familiarity with Kotlin's unique features that aid in producing robust, crash-resistant applications, which is a significant asset for any organization.

4. Can you explain extension functions in Kotlin?

Extension functions enable developers to extend classes without inheritance, promoting code reusability and clean code principles.

Evaluating a candidate's knowledge in this area helps ensure that they can write more concise, readable code, and can take advantage of Kotlin's powerful features to streamline development.

5. How does the when expression work in Kotlin?

The when expression is more powerful and flexible than switch statements found in other languages. Understanding this demonstrates a developer's familiarity with Kotlin-specific control flow structures. This knowledge is crucial to write clean and efficient Kotlin code.

6. What are Coroutines in Kotlin, and when might you use them?

Coroutines are a fundamental aspect of Kotlin programming, especially for tasks that require handling long-running tasks without blocking the main thread, like network requests.

A developer who understands coroutines can write highly responsive and user-friendly Android applications.

7. What are the differences between List, Set, and Map in Kotlin?

A firm grasp of Kotlin's collection types—List, Set, and Map—is essential for data manipulation in any programming task.

This question allows the interviewer to assess a candidate's understanding of these data structures and their appropriate usage, crucial for writing efficient algorithms and handling complex data in a Kotlin-based application.

8. What is a Companion Object in Kotlin?

A solid understanding of Companion Objects signifies a candidate's knowledge of how Kotlin handles static behavior, which is different from many other OOP languages.

It's a vital concept for object-oriented programming in Kotlin, providing static utility functions or constants related to the class. The use of Companion Objects can affect the structure and organization of the codebase.

9. Can you describe the difference between a suspend function and a regular function in Kotlin?

Asynchronous programming is a key skill for Android developers and suspend functions are at the heart of Kotlin's approach to managing asynchronous tasks with coroutines.

A solid understanding of this topic ensures that a developer can create non-blocking, responsive applications, significantly enhancing the user experience.

10. Can you describe a time when you had to learn a new programming language or technology to complete a project?

Kotlin developers often need to stay up-to-date with the latest technologies. This question assesses adaptability and learning agility.

A developer’s ability to learn and adopt new technologies signifies their potential to grow and contribute as the tech landscape evolves.

11. Tell us about a time when you disagreed with a team member about a coding or design decision.

Software development often involves differing opinions.

This question evaluates the candidate's conflict resolution and communication skills, crucial for maintaining a healthy, collaborative team environment.

It can also reveal their approach to problem-solving and respect for diversity of thought.

12. How do you balance the need for meeting deadlines with ensuring high-quality, clean code?

This question explores the candidate's sense of responsibility and their approach to quality vs. speed.

It tests their ability to manage time effectively and deliver high-quality work under pressure.

It also provides insight into their work ethic, diligence, and commitment to excellence.

13. Can you tell us about a time when you had to work under pressure to meet a tight deadline?

This question assesses the candidate's stress management skills and ability to deliver quality work within constrained timelines.

It reveals their ability to prioritize tasks and maintain focus under pressure, which are key attributes in fast-paced software development environments.

14. Describe a situation where you had to collaborate with a difficult team member.

This question is designed to understand the candidate's interpersonal skills and ability to handle conflict.

It provides insights into their emotional intelligence, patience, and ability to maintain professionalism in challenging circumstances. These skills are essential for fostering a positive, collaborative work environment.

15. Can you share an example of when you took the initiative to solve a problem or improve a process at work?

By asking this question, you can assess a candidate's proactive approach and their willingness to go beyond their defined role for the betterment of the project or the team. Such initiative is highly valued in a Kotlin developer as it can lead to code optimizations, better solutions, and process improvements.

Is there another way to assess Kotlin skills?

While the interview questions provide valuable information about a candidate's skills, adding a Kotlin skills test can further enhance the hiring process.

Combining the interview questions with a Kotlin skills test creates a comprehensive evaluation process that assesses both theoretical knowledge and practical coding skills.

The results of the Kotlin test provide concrete evidence of a candidate's proficiency in Kotlin, enabling you to make more informed decisions based on quantifiable data.

Check out our Kotlin test page to find out how it works.