Chapter 1: Introduction to Kotlin Interview Questions

Greetings! Following the positive response to my previous article, I am excited to continue the series with a new set of essential Kotlin interview questions that every developer should be familiar with in 2024.

Whether you are preparing for an upcoming interview or simply wish to assess your developer knowledge, I encourage you to challenge yourself with these questions! It should only take about five minutes of your time, and I assure you it will be worthwhile.

Kotlin has become the favored language for Android development. What makes it so special? The language boasts a modern, succinct syntax along with built-in features that help prevent frequent programming errors, such as null pointer exceptions. According to Google, over 60% of professional Android app developers now utilize Kotlin.

Chapter 2: Key Kotlin Interview Questions for 2024

Ready to dive in? Let’s get started!

Q1: What distinguishes primary constructors from secondary constructors in Kotlin?

In Kotlin, the primary constructor serves as the main constructor of a class, defined within the class header and responsible for initializing the class properties.

Here’s an example:

class MyClass(val param1: String, val param2: Int) {

fun print() {

println("$param1 and $param2")

}

}

fun main() {

val obj = MyClass("Kotlin", 10)

obj.print() // Output: Kotlin and 10

}

On the other hand, secondary constructors are additional constructors that can be defined within a class, allowing for various ways to instantiate objects with different parameter sets. They are declared using the constructor keyword.

Example:

class MyClass {

val param1: String

val param2: Int

constructor(param1: String, param2: Int) {

this.param1 = param1

this.param2 = param2

}

fun print() {

println("$param1 and $param2")

}

}

fun main() {

val obj = MyClass("Kotlin", 10)

obj.print() // Output: Kotlin and 10

}

Q2: How do the "==" and "===" operators differ in Kotlin?

In Kotlin, the "==" operator checks for structural equality, while "===" checks for referential equality.

Structural equality ( "==" ) assesses whether two objects share the same structure or content:

fun main() {

var a = "hello"

var b = "hello"

var c = null

var d = null

var e = d

println(a == b) // true

println(a == c) // false

println(c == e) // true

}

Referential equality ( "===" ) verifies the memory addresses of two objects to determine if they point to the same instance:

fun main() {

var a = "Hello"

var b = a

var c = "world"

var d = "world"

println(a === b) // true

println(a === c) // false

println(c === d) // true

}

Q3: Can you explain the difference between lateinit and lazy initialization in Kotlin?

Both lateinit and lazy are used to postpone variable initialization until needed, though they are applied in different contexts and have notable distinctions:

• lateinit is specifically for mutable properties (var). Variables marked with lateinit must be non-nullable and should be initialized before use.

Example:

class MyClass {

lateinit var name: String

fun initialize() {

name = "John"

}

fun printName() {

println(name)

}

}

fun main() {

val obj = MyClass()

obj.initialize()

obj.printName() // Prints "John"

}

• lazy is intended for immutable properties (val). A variable marked as lazy is only computed upon first access, and subsequent accesses will return the previously computed value.

Example:

fun main() {

val myString: String by lazy {

println("Computing the value")

"Lazy Initialization"

}

println("Before accessing lazy property")

println(myString) // Prints "Computing the value" and "Lazy Initialization"

println("After accessing lazy property")

println(myString) // Prints "Lazy Initialization" (value is not recomputed)

}

Q4: What is the distinction between the "let" and "apply" scope functions in Kotlin?

Both let and apply are scope functions that allow operations on an object within a specific context, though they fulfill different roles.

• let is a scope function enabling operations on a non-null object within a lambda expression, commonly used for null-checks and executing additional operations. The output of the let function is the result of the lambda expression.

Example:

fun main() {

val name: String? = "John"

val result = name?.let {

it.length

}

println(result) // Output: 4

}

• apply is used to configure an object by providing a lambda expression as a receiver, often for initializing or setting up objects. The output of the apply function is the object itself.

Example:

data class Person(var name: String, var age: Int)

fun main() {

val person = Person("John Doe", 25).apply {

age += 5

}

println(person) // Output: Person(name=John Doe, age=30)

}

Q5: What is the purpose of the with function in Kotlin?

The with function in Kotlin is a scope function that allows operations on an object within a specific context, removing the need to repeatedly reference the object. It simplifies code when multiple operations on the same object are required.

Example:

fun main() {

val person = Person("John", 25)

with(person) {

println("Current person: $this")

age += 1

println("After a year: $this")

}

println("Final person: $person")

}

Looking for more information? Be sure to check out the first part of this series if you haven't done so already. Feel free to leave a comment to let me know if you'd like more articles like this one! Don't forget to follow me and share this with fellow Kotlin enthusiasts.

In this video, you'll discover Android and Kotlin interview questions that are crucial for your preparation!

This video covers top Kotlin interview questions and answers, perfect for mastering your understanding and readiness for interviews!