Top 10 Kotlin Interview questions

11 Jan 2023, 20 Questions

If you are about to attend the Kotlin interview it is highly recommended that you go through the advanced Kotlin interview questions for your reference. Kotlin is one of the latest JVM programming languages and Google has also declared it is the official language for Android development aligned with Java. It is also suitable for developing server-side applications through which a developer can build and execute expressive coding. Kotlin also supports Android application development functioning hence there is a wide range of scope learning the same. If you are looking for a parcel of opportunities from all across the organization then polish your skills and consider the resources.

Advantages of Kotlin
  • This language is quite similar to Java hence it is quite easy to learn
  • This application can be used on various devices and desktops. it also includes web service and mobile phones
  • Kotlin refers to a functional language which is entirely based upon Java Virtual Machine, it helps in code optimization.

Kotlin supports multiple programming paradigms, such as internal, object-oriented, and functional programming. Our collection of Kotlin Interview Questions shall help you to understand the basics of this language.

Android kotlin interview questions and answers

Here in this article, we will be listing frequently asked Kotlin Interview questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q1. What’s the difference between lazy and lateinit?
Lateinit Lazy
It is late initialization It is lazy initialization.
It can be initialized from anywhere in the object It can be initialized only from the lambda function.
It can only be used for var type. It can only be used for Val type.
Multiple initializations are possible in lateinit. Only a single initialization is allowed here.
It is not allowed in properties of primitive types. It is allowed on properties of primitive types.
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Q2. Which one is better kotlin or Java?

Although both Java and Kotlin are used for Android app development, it is hard to choose a better one. This is because both have their pros/cons and are dominant programming languages.

Advantages of using Java:

  • It has a straightforward and readable syntax.
  • It is a pure form of OOPS
  • It has a faster compilation speed than Kotlin
  • Some features of Android studio, like auto-complete and compilation, run faster.

Advantages of using Kotlin:

  • It is comparatively easy to learn than Java
  • It does not have the legacy baggage that Java has been carrying around for a long time.
  • It is packed with modern programming features, making development a lot easier.
  • It has a safer and smarter compiler as compared to Java.

As you can see, both of these languages have their advantages and disadvantages. So, the actual question you must be asking yourself is, what are my needs and what’s best for my project.

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Q3. Can you execute Kotlin code without JVM?

Yes, you can execute a Kotlin code without the help of a JVM.

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Q4. How does string interpolation work in Kotlin?

String interpolation is a variable substitution having its value inside a string. In Kotlin, the $ character is used for interpolating a variable, and the ${} is used to interpolate an expression. Kotlin allows users the liberty of accessing variables and expressions directly from the string literals, thus eliminating the need for concatenation.

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Q5. What do you understand by Kotlin, explain its working?

Kotlin is an open-source programming language that entirely runs over the virtual machine for its proceeding. This language executes utilizing the Java platform and it was developed by JetBrains. This language is quite simpler than most of its variants specially Java.

All of its codes are converted into native quotes that are processed by the byte code conversion where it refers to the object-oriented programming language.

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Q6. Why Kotlin is better than Java?
As Kotlin is an open-source programming language it significantly refers to a general language serving all the purposes. It also offers code redundancy in which most of the features are included which are not available in Java. It is also a perfect combination of features like null safety, primary constructors, extension functions, properties, inline expressions, lambda expressions and various other types of interference are included in it. Kotlin also serves for all the major properties and its variables.
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Q7. What do you understand by structural expressions?

Structural expressions refer to the representative form of the loops in Kotlin. There are three important expressions which are:

  • Break- this expression helps the user to break the nearest enclosing loop
  • Return- this expression helps the user to return the nearest functions or any other default functions.
  • Continue- this expression helps the user to proceed further for the next loop.

If you are looking for a decent set of questions then you can categorize it under the best Kotlin interview questions for experienced professionals.

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Q8. Please elaborate on the modifiers in Kotlin?

Developers which are used to personalize declarations are known as modifiers and there are four types of modifiers available in Kotlin.
These modifiers are

  • Public- all the declarations are visible here
  • Internal- it uses the declarations present on specific locations
  • Private- declarations are contained in restricted files
  • Protected- here declarations are secured and usually not available for top-level declarations.
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Q9. Can you mention some of the extension methods used in Kotlin?

Some of the significant extension methods used in Kotlin are-

  • Read texts () - it is helped to read the content present in files to a single string
  • Buffer reader () - it is used to read the files to buffer reader
  • Read each line () - it is used to read the lines by the following line after line
  • Headlines () - it helps to read the content for listing.
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Q10. What do you understand by data class in Kotlin?

The classes which are used to hold the data or content are known as data classes. Earlier these data classes were only used to build the codes in Java but following the explicit implementation of its higher and greater set of properties, it is significant in kotlin as well. Along with this language, functions like tostring, equals are also combined with it. Kotlin offers a variety of these functions by implementing them along with the component functions.

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Q11. Mention the type of strings present in Kotlin?

Basically, strings refer to a collection of various characters altogether. There are two types of strings present in Kotlin which are-

  • Raw strings
  • Escaped strings

Under these strings, templates can also be evaluated easily and this evaluation is known by term as string template interpolation.

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Q12. List down the basic data types in Kotlin?

Data types are the instances of consonants or variables tending to decide the type of variable. It also specifies the space required for the storage of these variables.

The data types are-
  • Numbers
  • Characters
  • Strings
  • Arrays
  • Booleans

Note: This is one of the significant kotlin interview questions asked in most interviews.

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Q13. What are constructors, explain its types?

There are two types of constructors in Kotlin which are-

  • Primary constructor- It is a specific section of class header and mostly it is always declared after the class name.
  • Secondary constructor- This section of the constructor is always declared inside the class.
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Q14. What is the difference between inline and infix functions?

Inline Functions

Used to prevent the object allocations for the functions or lambda expressions that have been called.

Infix Functions

It is used for calling functions without any parentheses or brackets.

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Q15. How to create empty constructor for data class in Kotlin?

If you give default values to all the primary constructor values, you shall automatically create an empty constructor for data class.

For example, if you have a data class like this:

data class Activity(
   var updated_on: String,
   var tags: List,
   var description: String,
   var user_id: List,

And you want to initialize the data class with an empty constructor, all you have to do is assign the default values to all the primary constructors, like this:

data class Activity(
   var updated_on: String = "",
   var tags: List = emptyList(),
   var description: String = "",
   var user_id: List = emptyList(),

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Q16. How to initialize an array in Kotlin with values?

Here’s how to initialize an array in Kotlin.


val numbers: IntArray = intArrayOf(11, 12, 13, 14, 15)

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Q17. Where should I use var and where val?

In Kotlin, you should use var where the value of the variable is changing very frequently. A good example would be getting the location of an android device: var integerVariable : Int? = null

Whereas, Val should be used in a case where there would be no change of value throughout the whole class. For example, setting the value of text view or maybe a button’s text through code:

val stringVariables : String = "Button's Final Text"

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Q18. How to create singleton class in kotlin?

Here is the best way to create a singleton class in Kotlin:


enum class Singleton {


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Q19. What is a purpose of Companion Objects in Kotlin?

In Kotlin, if you need to write a code for a function that can be called without a class instance but it needs access to the internals of a class, you can use a companion object declaration in that specific class.


class EventsManager {
    companion object FirebasesManager {     
val firebasesManager = EventsManager.FirebasesManager

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Q20. What’s Null Safety and Nullable Types in Kotlin?

Null safety, also known as void safety is a guarantee that no object references shall have null or void values.

Nullable types in Kotlin are a type of reference which are declared by putting a “?” behind the String.

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kotlin android interview questions have always helped the experience’s to build their career in Kotlin's development and functioning. The references are incredibly marked for students to grow their careers exponentially with reputed organizations. Kotlin is preferred as a general-purpose programming language which is also a cross-platform service having type interference. Using Kotlin is convenient and safe to use and code also it is interoperable. Due to its utility, most of the organizations are actively hiring Kotlin professionals. This article actively contains Android kotlin Interview Questions who are willing to build their career in Kotlin.

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