Kotlin Interview Questions

Kotlin has in recent years mobile and web applications have become a popular language in development. This language, emerging as the modern alternative to Java, offers developers cleaner, more understandable and less code with the ability to work with. Android development being supported by Google further increases the importance of Kotlin.

If you are preparing for a Kotlin interview, you need to understand the basics of this language well. Basic concepts like variables, functions, classes, inheritance, and more are among the topics you might frequently encounter in interviews. Knowing well how Kotlin works, its advantages, and its areas of use is one of the keys to your success in the interview.

Learning Kotlin is not only an important investment for interviews but also for the progress of your software development career. Learning this language helps you become more efficient and effective in mobile application development. Therefore, when preparing for a Kotlin interview, do not just memorize questions and answers; focus on understanding the language deeply and applying it. This will not only help you succeed in the interview but also in real-world projects.

Kotlin Interview Questions and Answers

1. What are the advantages of Kotlin over Java?

• ✅ Less Errors: The probability of errors in Kotlin is lower compared to Java.
• ✅ Easy Process: Kotlin automatically handles everything through classes, simplifying the process.
• ✅ Extension Support: Kotlin offers strong support for extension functions.
• ✅ Rewriting Process: Rewriting getter and setter methods in Kotlin takes much less time.

2. How do you distinguish between Val and Var declarations?

Variables defined with "val" are immutable, while variables defined with "var" can be reassigned.

3. Is it possible to convert a String to an Int in Kotlin?

Yes, it is possible to convert a String to an Int using the “toInt()” method.

4. What is Null Safety in Kotlin?

Understanding and explaining Kotlin's null pointer exception prevention mechanism is important. Null safety is one of Kotlin's strongest features and includes structures like the “?, !!” operators and “?.let { ... }”.

5. What is the advantage of Data Classes in Kotlin?

Data classes are used to reduce boilerplate code and easily create data transfer objects (DTO). Their features automatically generate functions like equals, hashCode, and toString.

6. How are Extension Functions used in Kotlin?

Understanding how to define and use extension functions is a powerful feature that Kotlin offers for adding new methods to existing classes. This allows you to add new functions to a class without modifying the existing class.

7. What are Kotlin Coroutines used for?

Coroutines are one of the keys to managing long-running operations more efficiently in Kotlin.

8. What is the Elvis Operator?

The Elvis Operator (?:) is used to safely unwrap a nullable value.

9. What are Nullable Types in Kotlin?

In Kotlin, nullable types are types like String?, Int?, Float?, etc.

10. What is the difference between const and val in Kotlin?

const can only be used with val and only for compile-time constants. It cannot be used with local variables.

11. How do you indicate that a function is defined in Kotlin?

The return type of a function is specified after the ":" symbol. 

12. What is the difference between the == and === operators in Kotlin?

The == operator checks if the values are equal. The === operator checks if the references are the same.

13. What are the types of constructors in Kotlin?

Constructors in Kotlin can be defined as two types: primary and secondary: 

• 👉 Primary: Primary constructors are emphasized in the class headers. They cannot contain any logic. Therefore, only one primary constructor exists for each class.
• 👉 Secondary: Secondary constructors are defined in the class body. They can contain logic. Multiple secondary constructors can be specified.

14. How does String Interpolation work in Kotlin?

String Interpolation is used to evaluate string templates. The $ symbol is used to insert variables within a String.

15. Is there a 'new' keyword in Kotlin?

'new' keyword does not exist in Kotlin. However, it exists in Java.

16. How is a class object instantiated in Kotlin?

class A

var a = A()

Val new = A()

17. What is the difference between the 'open' and 'public' keywords in Kotlin?

Open means open to extension. In Java, methods are overridable by default. In Kotlin, to make a method overridable, 'open' must be used, but this cannot be done by default. 

If no visibility modifier is specified in Kotlin, 'public' is used by default. This means that declarations are accessible everywhere in the program.

18. What does the 'when' keyword mean in Kotlin?

'when' keyword replaces the switch operator in other languages. It allows for a specific code block to be executed when a certain condition is met.

Recommended Resources to Prepare for Your Kotlin Interview

Preparing for a Kotlin interview not only involves learning the basics of the language but also requires understanding advanced concepts. Here are some recommended resources you can benefit from while preparing for a Kotlin interview:

1. Kotlin Documentation: The official Kotlin documentation comprehensively covers everything from the basics of the language to advanced features. Especially for beginners, the "Kotlin Koans" section allows learning through practice.
2. Kotlin in Action: Written by one of the creators of Kotlin, this book comprehensively covers the basics of the Kotlin language, idiomatic uses, and advanced features. The book is filled with real-world examples and offers a practical learning experience.
3. Kotlin Courses on Coursera: Kotlin courses on online learning platforms help you learn the language through video lessons and practical projects. These courses offer knowledge at various levels, from beginner to advanced.
4. GitHub Projects and Open Source Codes: Seeing how Kotlin is used in real-world projects reinforces the learning process. Open source Kotlin projects on GitHub help you understand practical uses of the language.
5. Stack Overflow and Kotlin Forums: Stack Overflow and official Kotlin forum pages are excellent resources for getting information on any problems you encounter or topics you are curious about. Answers given by experienced developers provide insights into the depths of the language.

Next Step

Before the Kotlin interview, first clarify all the basic concepts. Many of the questions asked in the interview test your fundamental knowledge of Kotlin. Second, practice! Don't just review the theory, apply Kotlin. The more you use Kotlin, the better you will understand its concepts and various uses.

During the interview, it's important to demonstrate that you can apply your knowledge not only theoretically but also practically. This approach will help you succeed in the Kotlin interview and also become an effective Kotlin developer in real-world projects.

If you want to learn Kotlin and build a career, Kotlin Bootcamps can teach you a lot. Coderspace Bootcamps help you specialize in this field. If you want to improve your software development skills, we recommend you check out our Bootcamps.