Top Kotlin Interview Questions You Must Know in 2023

Hey there! This post will walk through some common Kotlin interview questions any developer should know in 2023.

Whether you’re getting ready for an interview or simply want to test your skills, try answering these questions to challenge yourself!

Introduction

Kotlin is Google’s preferred language for Android development. Why? Because it offers a modern, concise syntax with built-in features that prevent common programming mistakes (such as null pointer exceptions). According to Google, Kotlin is used by over 60% of professional Android app developers.

Top Kotlin Interview Questions in 2023

Ready? Let’s get started!

Q1: What is the Elvis Operator?

The Elvis Operator (?:) in Kotlin is a shortcut for dealing with situations where a value might be null. Instead of writing an if-else statement, you can use the Elvis operator to quickly say, "Use this value if it's not null, otherwise, use this default value." It makes your code shorter and easier to understand.

val nullableValue: String? = null
val result = nullableValue ?: "Default Value"
println(result)

Q2: What is the difference between “const” and “val”?

val Is used to declare immutable variables. You can't change it later once you assign a value to it. It’s like a one-time assignment.

const Is used to assert compile-time constants, meaning their value has to be assigned during compile time. It is only allowed to initialize const val with String or primitive types.

val age = 35
const val appName = "My App"

Q3: What is the “lateinit” modifier and when do you use it?

The lateinit modifier indicates that a class's non-null property will be initialized at a later point. This is useful for properties that can't be assigned a value immediately in the constructor or when declared, but you know for sure they will be given before they are used.

lateinit var myString: String

fun myFunction() {
  myString = "Interview"
  println(myString)
}

Q4: What is the !! operator, and when do you use it?

The not-null assertion operator !! converts a value to a non-null type and throws an NullPointerException if the value is null. Developers should use it only when they are 100% sure that the value is not null.

var name: String?
name = null
println(name!!)

Q5: What is the difference between the “List” and “Array” types?

Both Array and List are ordered collections of elements where each element has a unique index. But keep in mind that:

• Unlike (Mutable) Lists, Arrays have a fixed size determined when they are created, and this size cannot be changed.
• Array is mutable, whereas List is not.

val ages: Array<Int> = arrayOf(25, 30, 22, 40)

val numbers: List<Int> = listOf(1, 2, 3, 4, 5)

Looking for more?

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Cheers!