Kotlin Interview Questions And Answers

Kotlin Interview Questions And Answers prepared from Codingcompiler experts. These Kotlin Interview Questions were asked in various interviews conducted by top multinational companies across the globe. We hope that these interview questions on Vagrant will help you in cracking your next job interview. All the best and happy learning.

In this article, you’ll learn

  • Kotlin Interview Questions
  • Kotlin Interview Questions And Answers
  • Advanced Kotlin interview Questions And Answers
  • The Best Kotlin Interview Questions And Answers


Kotlin Interview Questions

  1. What is Kotlin?
  2. What’s a const? How does it differ from a val?
  3. Does Kotlin allow us to use primitive types such as int, float, double?
  4. What is basic difference between fold and reduce in Kotlin? When to use which?
  5. What’s the difference between val and var declaration? How to convert a String to an Int?
  6. What is a data class in Kotlin?
  7.  What’s the difference between val and var declaration? How to convert a String to an Int?
  8.  Does Kotlin allow us to use primitive types such as int, float, double?
  9. How is !!different from ?. in unwrapping the nullable values? Is there any other way to unwrap nullable values safely?
  10. How is !!different from ?. in unwrapping the nullable values? Is there any other way to unwrap nullable values safely?


Kotlin Interview Questions And Answers


Q. What is Kotlin?

Ans: Kotlin is the latest general-purpose programming language from JetBrains with the type interference. It is totally interpolated with the JVM and also combines javascript or code.

Google officially promoted kotlin on Android for mobile development.  Kotlin is considered as a substitute to the standard java compiler.

Q. What’s a const? How does it differ from a val?

Answer: By default val properties are set at runtime. Adding a const modifier on a val would make a compile-time constant.

A const cannot be used with a var or on its own.
A const is not applicable on a local variable.

Q. Does Kotlin allow us to use primitive types such as int, float, double?

Answer: No kotlin does not support primitive datatypes as like in java. At the language level, we cannot use the above-mentioned types. But the JVM bytecode that’s compiled does certainly have them.

Q. What is basic difference between fold and reduce in Kotlin? When to use which?

Answer

  •  fold takes an initial value, and the first invocation of the lambda you pass to it will receive that initial value and the first element of the collection as parameters.
  • listOf(1, 2, 3).fold(0) { sum, element -> sum + element }
  • The first call to the lambda will be with parameters 0 and 1.
  • Having the ability to pass in an initial value is useful if you have to provide some sort of default value or parameter for your operation.
  • reduce doesn’t take an initial value, but instead starts with the first element of the collection as the accumulator (called sum in the following example)
  • listOf(1, 2, 3).reduce { sum, element -> sum + element }
  • The first call to the lambda here will be with parameters 1 and 2.

Q. What’s the difference between val and var declaration? How to convert a String to an Int?

Answer

val variables cannot be changed. They’re like final modifiers in Java. A var can be reassigned. The reassigned value must be of the same data type.

fun main(args: Array<String>) {
val s: String = “Hi”
var x = 5
x = “6”.toInt()
}

We use the toInt() method to convert the String to an Int.

Q. What is a data class in Kotlin?

Answer:

We frequently create classes whose main purpose is to hold data. In Kotlin, this is called a data class and is marked as data:

data class User(val name: String, val age: Int)

To ensure consistency and meaningful behavior of the generated code, data classes have to fulfill the following requirements:
The primary constructor needs to have at least one parameter;
All primary constructor parameters need to be marked as val or var;
Data classes cannot be abstract, open, sealed or inner.

Q. What’s the difference between val and var declaration? How to convert a String to an Int?

Answer: val variables cannot be changed. They’re like final modifiers in Java. A var can be reassigned. The reassigned value must be of the same data type.

fun main(args: Array<String>) {
val s: String = "Hi"
var x = 5
x = "6".toInt()
}

We use the toInt() method to convert the String to an Int.

Q. Does Kotlin allow us to use primitive types such as int, float, double?

Answer: At the language level, we cannot use the above-mentioned types. But the JVM bytecode that’s compiled does certainly have them.

What’s the entry point of every Kotlin Program?

The main function is the entry point of every Kotlin program. In Kotlin we can choose not to write the main function inside the class. On compiling the JVM implicitly encapsulates it in a class.

The strings passed in the form of Array<String> are used to retrieve the command line arguments.

Q. How is !!different from ?. in unwrapping the nullable values? Is there any other way to unwrap nullable values safely?

Answer: is used to force unwrap the nullable type to get the value. If the value returned is a null, it would lead to a runtime crash. Hence a !! operator should be only used when you’re absolutely sure that the value won’t be null at all. Otherwise, you’ll get the dreaded null pointer exception. On the other hand, a ?. is an Elvis Operator that does a safe call.

We can use the lambda expression let on the nullable value to unwrap safely as shown below.

Here the let expression does a safe call to unwrap the nullable type.

Advanced Kotlin interview Questions And Answers

Q. What’s the difference between == and === operators in Kotlin?

Answer: == is used to compare the values are equal or not. === is used to check if the references are equal or not.

Q. List down the visibility modifiers available in Kotlin. What’s the default visibility modifier?

Answer: 

public
internal
protected
private
public is the default visibility modifier.

Q. Is New a keyword in kotlin?

Ans: “New” is not a keyword in kotlin. We can initiate a new class as follow:

class  x
var  x  =  x()
val  new = x()

Q. What is mean by init block?

Ans: Init is a login block and it is executed in the primary constructor and initialised. If you want to revoke in the secondary constructor then it starts working after primary constructor in the chain form.

Q. Is inheritance compile in Kotlin?

Ans: Formal inheritance structure does not compile in the kotlin. By using open modifier we can final classes.

open  class B
{
}
class  c = B(){
}

Q. What are the class members in kotlin?

Ans: A class in kotlin have the following members:

  • Initializer blocks
  • Properties
  • Open declarations
  • Nested  classes
  • Inner classes

Q. List out some of the extension methods in kotlin?

Ans: Some of the extension methods are:

  • read Text(): Helps to read content in the files to a single string.
  • buffer Reader(): It is used to read contents of the file to buffer reader
  • read each line(): It reads each line by line in the file
  • readlines(): It helps to read lines of file for listing

Q. What is mean by init block?

Ans: Init is a login block and it is executed in the primary constructor and initialised. If you want to revoke in the secondary constructor then it starts working after primary constructor in the chain form.

Q. Explain Higher-Order Functions in Kotlin?

Answer: Higher-Order Functions: A higher-order function is a function that takes functions as parameters, or returns a function

The Best Kotlin Interview Questions And Answers

Q. Where does the Kotlin run and what is the entry point of Kotlin?

Answer: The Kotlin program once compiled, can run on standard JVM like other programming codes.And, like many other programming languages main() function is the entry point of the Kotlin.

Q. What are the different types of constructors in Kotlin?

Answer: There are two types of constructors in Kotlin:

Primary constructor: It is a section of the Class header and is declared after the class name.
Secondary constructor: This constructor is declared inside the body.

Note: There can be more secondary constructors for a class.

Q. Can you execute Kotlin code without JVM?

Answer: JVM, which stands for Java Virtual Machine is a feature of Kotlin. This feature compiles a Kotlin code into a native code, which can be done without JVM too.

Q. Mention the structural expressions in Kotlin?

Answer: There are three Structural expressions in Kotlin.They are:

  • Return: It returns from the nearest enclosing function or anonymous function by default.
  • Break: This expression terminates the closest enclosing loop.
  • Continue: This expression proceeds you to the next closest enclosing loop

Q. ) Can you migrate the code from Java to Kotlin? If yes how do you do it?

Answer: Yes, we can migrate the code from Java to Kotlin.This can be done using JetBrains IDEA, which facilitates the conversion of Java code to Kotlin code.

Q. Why Use Kotlin in Mobile App Development?

Answer: Since Kotlin simplifies many syntactical elements of Java, it’s easier to write concise, well-documented code. Additionally, since it runs directly on JVM, enterprises hardly need to invest in new tech stacks. So the cost-benefit adjustment is excellent.

Moreover, Kotlin has already started to replace many Java-based Android apps, alongside iOS apps written in Swift. This number will only increase over time and adapting to Kotlin will become a must for modern enterprises. So, to stay ahead of the competition, developers should embrace Kotlin today.

Q. What is the Function of the Elvis Operator?

Answer: The Elvis operator in Kotlin allows app developers to handle null-based exceptions. It is a compelling feature of Kotlin which enables programmers to reduce runtime crashes by a considerable margin. Although you can still handle your nulls yourself, the Elvis operator makes it relatively straightforward.

val z = x ?: return y

In this line, z will only contain the value of x if it is not null. Otherwise, the entire expression will halt executing and return y. It works since the return statement is also an expression. So, Elvis operator’s look like a ?: b in Kotlin.

Q. Why doesn’t Kotlin Feature Macros?

Answer: Macros are useful in a number of programming scenarios. However, they tend to create a mess of your project and often confuse new developers. This is why JetBrains, the developers behind Kotlin omitted this feature altogether. Moreover, developers often find it hard to test or optimize codebases that contain a lot of macros. So, omitting macros is a design decision. Ther developers of Kotlin are, however, working on features like serialization and compiler plugins to address some shortcomings of this decision

Q. Describe For Loops in Kotlin

Answer: Loops are a crucial programming construct that allows us to iterate over things as our program requires. Kotlin features all the commonly used loops such as for, while, and do-while. We’re describing the for loop in a nutshell in the following section.

val sports = listOf("cricket", "football", "basketball")
for (sport in sports) { // for loop
println("Let's play $sport!")
}

The above snippet illustrates the use of the for loop in Kotlin. It’s quite similar to Python and Ruby.

Q. What are the Kotlin Data Classes?

Answers: Kotlin offers a convenient way of storing values by means of the data class. A data class comes with many useful in-built methods such as for copying, string representations, instance collections, and so on. Data classes are defined using the data modifier. Some auto-generated methods available to a newly created data class are – toString, equals, copy, hashCode, and componentN functions. The first method returns a string representation, equals check for equality among properties, and copy allows cloning.

Q. How to Create Volatile Variables?

Answer: Volatile variables are a compelling feature that enables programmers to control threads, and CPU time more effectively. Declaring a variable as volatile is quite easy and differs slightly than from Java.

@Volatile var name:String = “something”

Actually, volatile is not a keyword in Kotlin, as opposed to Java. Rather it is an annotation and makes each data write visible to all other threads immediately.

Q. What’s the Entry Point for Kotlin Programs?

Answers: Kotlin, like many popular programming languages, relies on a specific entry point. The main() function is this point, similar to other OOP languages such as C++ and Java. Developers can easily define the command-line arguments taken by Kotlin programs. For this, you’ll need to pass args: Array<String> to this main() function.

It takes a somewhat different syntax than traditional Java programs. Below we’re illustrating the differences between the main() function in both Java and Kotlin. You can easily compare them for a better understanding.

public static void main(String[] args) // Entry to Java Programs
fun main(args: Array<String>) // Entry to Kotlin Programs

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