Kotlin Interview Questions

Last updated on Nov 07, 2023

Kotlin is a leading programming language that has been developed by JetBrains. It has been declared as the official language to develop Android Applications by the tech giant Google.
Over the last couple of years, there has been an upsurge in the number of vacancies requiring Kotlin's knowledge. There is going to be an increase of 9.3% in the number of smartphone users across the world. This substantiates the statement that the world needs more Kotlin experts in 2020.
Over here, we have prepared a list of commonly asked Kotlin interview questions and answers. This interview guide on Kotlin is good for freshers as well as experienced professionals.
A thorough reading of these popular Kotlin interview questions is going to give you a good head start on your next Kotlin interview.

Most Frequently Asked Kotlin Interview Questions

1. What is Kotlin?

Ans: Kotlin is a powerful programming language that has been created to run on the JVM(Java Virtual Machine). It has been created by JetBrains, a very well-known IT organization acclaimed for building and developing great software apparatuses. You can type Kotlin statically and it offers an uncommon help for wholesome functional programming.
Moreover, Kotlin possesses the ability to resolve some critical issues looked by numerous Java developers, for example, invalid based blunders. It may very well be utilized for creating both Android as well as iOS applications close to universally useful programming. Because of its outrageous similarity with Java, designers can compose new highlights for their Java-based applications straightforwardly in Kotlin.

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2. What kind of programming is supported by Kotlin?

Ans: Kotlin can support two kinds of programming, namely

programming is supported by Kotlin

3. Is it possible to execute code in Kotlin without the usage of JVM?

Ans: Yes, it is possible to execute code in Kotlin without the usage of JVM. The purpose of JVM is to compile a given Kotlin code directly into native code. This process can be easily executed without the usage of JVM.

4. Why do you think one should choose Kotlin over Java?

Ans: Frequently hiring managers to pose such inquiries to gauge the profundity of the job searchers. Since contrasting two amazing programming languages can never hold up under productive outcomes, you ought to rather talk about their upsides and downsides for exhibiting your aptitude. Java is as yet a superior language that is used to create enterprise-grade customer applications because of its huge list of robust features and ceaseless network support. 

Be that as it may, despite being another language, it interoperates pleasantly with Java programming. It permits code developers to make inventive applications without composing many lines of code. Kotlin's solid type interfaces make it a strong decision for creating cutting edge applications. Additionally, since it very well may be likewise utilized for creating iOS applications, engineers don't have to grasp new stacks any longer.

5. Can you use primitive types for example- int, float, and double in Kotlin?

Ans: If I were to say at only the language level, we cannot use the afore-mentioned types. However, on the upside, the JVM’s bytecode which is compiled can surely have them.

6. What’s the entry point of every Kotlin Program?

Ans: It is the ‘main’ function that is an entry point of every program in Kotlin. In Kotlin we can decide not to compose the main function within the class. At the time of compiling the JVM implicitly encapsulates it within a class.
The string functions that are written as ‘Array’ are utilized to recover the order line arguments.

7. Why is it preferred to utilize Kotlin for a robust Mobile App Development?

Ans: As Kotlin improves numerous linguistic components of Java, it's simpler to compose a succinct and all around reported code. Furthermore, since it runs legitimately on JVM, enterprises scarcely need to put resources into new tech stacks. Therefore, the money-saving advantage is phenomenal.
Additionally, Kotlin has just begun to supplant numerous Java-based Android applications, and also the iOS applications written in Swift. This scenario will just increment after some time and adjusting to Kotlin will turn into an unquestionable requirement for present-day endeavors. Along these lines, to remain in front of the opposition, mobile app developers should grasp Kotlin today.

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8. What kinds of visibility modifiers can you find in Kotlin?

Ans: There are four kinds of visibility modifiers that are available in Kotlin

 kinds of visibility

Name the visibility modifier that is available to you by default.
The public modifier is the modifier that is available to us by default. 
List down some great features of Kotlin
Here are some great features of Kotlin-

  • It is able to support both object's arranged and useful programming worldview. 
  • It gives simple to utilize lambda works that are inaccessible in Java. 
  • Maintenance of Kotlin is significantly modest and gives fantastic adaptation to internal failure. 
  • Allows creating Node.js applications and JVMs. 
  • It supplants a good support for non-concurring correspondence. 
  • Exceptional similarity with pre- existing codes of Java.

9. What do you gather by Null Safety?

Ans: Kotlin usually comes along with well in-built insurance against undesirable null references which permits it to be more fault-tolerant. It in this manner permits projects to diminish NullPointerExceptions during runtime and forestalls undesirable program crashes. This is a typical issue looked by most existing Java programming and causes misfortunes costing a huge number of dollars. This is regularly authored as Null Safety among Kotlin engineers.

10. What is the use of abstraction in Kotlin?

Ans: Abstraction is the most significant idea of Objected Oriented Programming. In Kotlin, reflection class is utilized when you recognize what functionalities a class ought to have. In any case, you don't know about how the user is executed or if the user can be actualized utilizing various techniques.

11. Elucidate on the functionality of Null safety along with its types in Kotlin?

Ans: Kotlin puts a great deal of weight behind invalid wellbeing which is a way to deal with forestalling the feared Null Pointer Exceptions by utilizing nullable types which resemble String?, Int?, Float? and so forth. These go about as a wrapper type and can hold invalid qualities. A nullable worth can't be added to another nullable or fundamental type of value. To be able to recover the fundamental kinds we have to utilize safe calls that open up the Nullable Types. On the off chance that on opening up, the worth is invalid we can decide to disregard or utilize a default an incentive.

12. Illustrate about an Elvis Operator in Kotlin.

Ans: An Elvis Operator is typically used to securely unpack the type value received from the Nullable.
We can represent it as ‘?:’ on the nullable type. 

The value that is towards the right-hand side is going to be used in case the nullable type value is null.

var str: String? = “JournalDev.com”

var newStr = str?: “Default Value”

str = null

newStr = str?: “Default Value”

13. Name the different sorts of constructors in Kotlin. Differentiate between them.

Ans: There are two types of constructors in Kotlin, they are Primary constructors and Secondary constructors.
Primary — these are characterized in the class headers. They can't hold any inputs of logic. It is possible to have just a single primary constructor for every class.

Secondary — they're characterized in the class's body. They should delegate to the primary constructor if it exists. These constructors can hold logic very easily. There can be more than one secondary constructor.

14. How will you execute an init block in Kotlin?

Ans: An ‘init’ is the primary class initializer block that a developer can use in Kotlin. It’s implemented only after a primary constructor has been successfully instantiated. In case you raise a secondary constructor, in that case, it functions only after the primary one just in the order of its composition in the development chain.

15. Can you call Java functions in Kotlin?

Ans: This is possible as Kotlin permits the software engineer to call the existing procedures of Java from inside a Kotlin program. Functions, for example, the getter and setter couple are spoken to as properties. Kotlin doles out Unit to each void worth that originates from a Java work. Along these lines, the Unit in Kotlin is void in Java code. You should get away from some keywords of Kotlin Java, however. Since keywords like is, in, and object are legitimate identifiers in Java, you'll have to get away from them in Java libraries utilizing the backtick (') character. Furthermore, Kotlin executes highlights like stage types and explanations to guarantee invalid security when calling outside Java capacities.

16. List out some features that are available in Kotlin but not in Java?

Ans: Here are some features of Kotlin that are unique to it and are not available in Java.  

features that are available in Kotlin

17. What is the way to declare a variable in Kotlin?

Ans: We can declare a variable in Kotlin by using val and var. here is an example of the same-

Here is an example of a standard declaration of a variable in Kotlin 

Val x: String = "Welcome"

var a = 9

18. What are some extensions that are available to java.io.file in the Kotlin environment?

Ans: Here is a list of some useful extensions that are available to java.io.file in the Kotlin environment 

File.bufferedReader() : this extension facilitates the reading of contents of a given file in the BufferedReader
File.forEachLine() : this extension facilitates the reading of a given file in a line by line manner in the Kotlin environment
File.inputStream() : this extension helps in reading of the given contents of a file to the InputStream
File.readBytes() : this extension facilitates the reading of the contents of a file to the ByteArray
File.readLines() : this extension facilitates to read the lines of a file to the List
File.readText() : this extension helps you in the reading of contents of a given file to a single String

19. What is the interoperability of Kotlin with JavaScript?

Ans: During numerous Kotlin inquiries questions, interviewees are gotten some information about the level of adaptability Kotlin takes into account JavaScript applications. Kotlin empowers Android and iOS devs to flawlessly target JavaScript. This means you can without much of a stretch trans-compile a Kotlin program to local JavaScript code. This permits code designers to effectively make programming for the famous Node.JS stage.

Kotlin empowers developers to control all components of JS programming, for example, controlling the DOM, utilizing illustrations, dealing with the server-side, etc. Furthermore, you can use Kotlin with existing JS libraries like jQuery and React.

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20. What do you mean by the Higher-Order Functions?

Ans: In Kotlin a higher-order function is a class function whose job is to take the functions as parameters or to return the value as a function. 

21. Why is there no feature of Macros in Kotlin?

Ans: Macros are helpful in various programming situations. Nonetheless, they will, in general, make a wreck of your extent and regularly confound new engineers. This is the reason JetBrains, the engineers behind Kotlin, precluded this component by and large. Besides, engineers frequently think that it's difficult to test or upgrade codebases that comprise a ton of macros. Along these lines, excluding macros is a plan choice. The code developers who work on Kotlin are, in any case, taking a shot at highlights like serialization and compiler modules to address a few deficiencies of this choice.

22. Highlight some advantages of Kotlin.

Ans: Some advantages of Kotlin are-

Kotlin is straightforward and simple to learn as its language structure is like that of Java. 

It is the practical language that depends on JVM (Java Virtual Machine), which expels the standard codes. Upon this, Kotlin is considered as an expressive language that is effectively clear and justifiable and the exhibition is generously acceptable. 

It tends to be utilized by any work area, web server or portable based applications.

23. Highlight some disadvantages of Kotlin.

Ans: Some of the disadvantages of Kotlin are-

Kotlin doesn't give the static modifier, which messes up ordinary java engineer. 

In Kotlin, the capacity presentation should be possible in numerous spots in the application, which makes it inconvenient for the designer to comprehend which capacity is being called.

24. What is the concept of Multiplatform?

Ans: Kotlin developers keep on turning out new and energizing highlights for engineers. The multiplatform highlight is one such exploratory component that empowers developers to share code between a few stages, for example, JavaScript, iOS, and work area applications. 

This is getting progressively well known among current designers since it lessens the measure of code by an impressive factor. You can utilize a significant part of the equivalent codebase for composing applications for various stages because of this element. Make a common module for your applications and rundown the conditions. Presently, you can make separate modules for various stages and coordinate the central functionalities utilizing the normal module.

25. Explain Nothing, Unit and Any?

Ans: In Kotlin, any is an information type that speaks to essential sorts like a whole number, buoys, and strings. Any sort can't hold any invalid qualities as a matter of course and executes programmed throwing of lower types. This is like the Java object java.Lang.Object. 

The unit type is a sort that is returned by work calls that don't bring anything back. Kotlin doesn't offer void capacities like C or Java do and uses unit for this reason. You can consider the unit only one explicit instance.

The nothing type is returned by Kotlin capacities when they can't arrive at the base of the capacity. It generally occurs because of vast recursions or loops.

26. What are the structural expressions of Kotlin?

Ans: In Kotlin there are three different types of structural expressions and they are as follows-

  • return – this type of structural expression pauses the program that is under execution and at the same time returns the value from the enclosed function.
  • break – this type of structural expression is generally used to terminate the nearest loop that is enclosing in Kotlin's environment.
  • continue – this type of structural expression allows the execution of the Kotlin code to go on to the next iteration of the loop leaving the execution of the current code under operation.

27. Explain the destructuring declarations.

Ans: Destructuring Declaration is a brilliant method to relegate different qualities to factors from information put away in objects/strings/arrays.

Inside paratheses, we've set the variable presentations. In the engine, destructuring assertions create component works for every one of the class factors.

28. What’s the difference between lazy and lateinit?

Ans: Both are utilized to postpone the property instatements in Kotlin 

lateinit is a modifier utilized with var and is utilized to set the incentive to the var at a later point. 

apathetic is a technique or rather a state lambda articulation. It's determined to a val as it were. The val would be made at runtime when it's needed.

Here is the command

val x: Int by lazy { 10 }

lateinit var y: String

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29. State the number string type you can get in Kotlin.

Ans: We have an option of two types of strings in Kotlin and they are-

number string type

30. What do you understand by interpolation of a string?

Ans: The process of creating a template in the string is call interpolation.

31. What is a Sealed Class in Kotlin?

Ans: Sealed classes are another incredibly valuable element of this cutting edge programming language. They can be utilized to limit the legacy progressive system of a class. You should simply characterize a class as fixed, and no one will have the option to make subclasses that have a place with this fixed class. 

These classes will prove to be useful when you use them inside when articulations. If you can impeccably cover every conceivable case, you won't need to utilize the else statement. In any case, recall that fixed classes are dynamic without anyone else and you cannot start up one straightforwardly.

32. What is the process of creating a Volatile Variable?

Ans: Volatile variable in Kotlin is a convincing element that empowers software engineers to control strings, and CPU time all the more successfully. Pronouncing a variable as unstable is very simple and varies somewhat from Java.

@Volatile var name:String = "something"

Unpredictable isn't a keyword in Kotlin, rather than Java. Or maybe it is a comment and makes every datum compose obvious to every other string right away.

33. What do you understand by the class members in Kotlin?

Ans: The following members are available in a class in Kotlin-

class members in Kotlin

34. Differentiate between Val and Var?


Val: Val, is the acronym used for the term value. This value is a constant and this cannot be changed once it is assigned.

Var: Var, is the acronym used for the term variable. A variable is a storage location that receives the relocation of values with the same kind of data types.

35. Why do we need the Object Keyword?

Ans: Kotlin gives an extra keyword called object near its standard item. In opposition to the customary article situated worldview where you characterize a class and make the same number of its cases as you are going to need, the object keyword permits you to make a solitary, slow execution. The compiler will make this object when you get to it in your Kotlin program.

36. What is the way towards managing a null operator?

Ans: The best way of managing a nullable value is by utilizing an Elvis operator.

37. How do you think extension functions are useful?

Ans: Extension functions Augmentation capacities assist with expanding a class with new usefulness without acquiring from the class. Likewise, you may utilize them like an inbuilt capacity for the class all through the application.

38. Is there any kind of additional functionalities that are available for standard Java packages and the standard Java classes?

Ans: Of course, Yes. Kotlin uses the concept of extension functions, that we already talked about, to build some useful and more widely used functions among developers directly into the Kotlin library.

39. How can you contrast two strings?

Ans: One can easily do that in two strings in two ways,
Using”==” operator”
sing compare() function

40. What are Coroutines?

Ans: The Kotlin coroutine is a light-weight string that doesn't require any setting turning on the processor and won't map on local strings. This is the motivation behind why they are quick in preparing the solicitations.

41) Define the Scope functions in Kotlin.

Ans. In Kotlin standard library, multiple functions are available that help carries out the code block within the object's context. Here, the temporary scope is developed when we utilize the lambda expressions to call such functions to an object known as Scope functions. Moreover, Scope functions make the code more engaging, clear, and brief, which represents the core features of Kotlin programming.

Scope functions in Kotlin language are of multiple types, such as:-

  • Let
  • Run
  • Apply
  • Also
  • With  

Let - In the let function, the context object is "it", and the value that returns is "lambda result". Generally, we use this function for null safety calls.

Run - In the run function, the context object is "this", and the value that returns is "lambda result". It combines the features of both let and with functions in Kotlin and is useful when the lambda object includes initialization and computation of the value that returns. Further, this function helps perform computations along with null safety calls. 

Apply - In the apply function, the context object is "this", and it returns the context object as a result. It is helpful to drive the receiver object members mainly to initialize them.

Also - The context object for the function also is "it", and the return value becomes the "context object". This function helps execute some additional activities after initializing the object members.

With - The context object for the function "with" is "it". It returns the "lambda result" as a return value. This function is proper when calling the functions without offering the lambda result.

42) What are the primary data types used in Kotlin language?

Ans. The data type for a variable or a constant plays a crucial role in Kotlin language, determining which variable type is proper and how much space it needs for storage. The following are the different data types that a string allows :-

  • Numbers
  • Strings
  • Arrays
  • Characteristics
  • Booleans

43) What do you mean by the Suspend function in Kotlin?

Ans. The suspend function in Kotlin is used to stop, start, and resume at any time. This function can perform long-running activities and remains on standby without blocking until it finishes. Moreover, the suspend function is called on only from other suspend functions or from a coroutine and not from a regular function. A suspending function can call any of the standard functions, but it needs another suspending function to suspend or eliminate the execution. Further, the suspend function is expressed as delay().

44) What is meant by Open Keyword in Kotlin?

Ans. In Kotlin, the Open Keyword refers to "open for extension". All functions and classes in Kotlin are final by default, and we cannot override or inherit them. Therefore, we use an empty keyword to obtain this before the class and functions.

45) Define Ranges operator in Kotlin?

Ans. In Kotlin language, the range operator supports iterating in the range. The range operator is available in the form of (..). The following is an example of it-

for (i in 1..15)  


The above example defines that it will give the outcome to print data from 1 to 15 numbers.

46) Define the Public keyword in Kotlin?

Ans. In Kotlin, the Public keyword is the visibility or default modifier that enables declarations to be visible and accessible everywhere. It is used when the visibility modifier is not stated.

47) What is meant by

Ans. When it is used in Kotlin as an expression or statement, it is often used instead of a switch. It is because it has a much better design and is more succinct and powerful to use than the legacy switch.

48) Define the use of @JvmStatic in Kotlin?

Ans. In Kotlin, @JvmStatic is an annotation proper to build static methods for functions and to inform the compiler that it is a static method. We can use it within the Java code.

49) Explain the use of @JvmFiled in Kotlin.

Ans. In Kotlin, @JvmFiled annotation helps to achieve compatibility between the two different languages. Further, it helps to access the Kotlin class fields from the Java code without needing any setters and getters.

50) What is meant by @JvmOverlaods?

Ans. The @JvmOverloads annotation is a proper function when we pass the default values similar to arguments from the Java code to the Kotlin code.

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51) What do you mean by Data classes in Kotlin?

Ans. Data classes help store some data in Kotlin and don't offer other features. The advantage of using Data class in Kotlin is that Kotlin provides a large amount of self-produced code, and it holds it without needing any boilerplate code in Java.

52) Explain the Double Bang operator in Kotlin.operator in Kotlin?

Ans. The double bang (!!) operator in Kotlin is applicable to transform any value into a non-null type. It also throws an exception called KotlinNullPointer exception when the value becomes null.

53) Define the Singleton class in Kotlin?

Ans. A Singleton class in Kotlin defines only a single instance that can be developed and used anywhere. Users can easily access the singleton object from their code through this class.

54) Can we use the word

Ans. We cannot use it as a keyword in Kotlin, but we can locate it within the Java language.

55) Define the use of Lambda Expression in Kotlin?

Ans. It is an expression without a name, and these expressions are frequently used with some higher-level functions, like a map.


With this, we come to the end of our Kotlin interview questions and answers. In this blog, we have discussed the popular interview questions that you might face in your interview on Kotlin.

Once you sit on to prepare for your Kotlin interview, don’t forget to read through this list of Kotlin interview questions and answers. This is simply because, when you see the familiar questions being asked to you in your interview, you are going to feel more confident and will clear your interview with much ease.

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