Kotlin Interview Questions

Kotlin has become one of the most popular ways to develop modern Android applications. Rapidly replacing Java, it offers a more readable and safer programming experience. For developers, learning Kotlin and effectively representing it in interviews is now essential. In this guide, we’ll cover the most critical topics like Kotlin interview questions, Kotlin Android interview questions, Kotlin coroutines interview questions, Kotlin backend interview questions, and Kotlin job interview questions with concise explanations.

1. What Are the Differences Between Kotlin and Java?

Key differences between Kotlin and Java:

• Null Safety: Kotlin eliminates null pointer exceptions using the ? operator; Java does not guarantee this.
• Extension Functions: Kotlin allows adding functions externally to classes.
• Data Classes: Kotlin generates constructor, getters/setters automatically with data class.
• Lambda Expressions & Functional Programming: Kotlin has a more functional style.

Kotlin Example (Null Safety):

val name: String? = null
println(name?.length) // Null check happens automatically

2. Kotlin Android Interview Questions: Activity, Fragment, Lifecycle

• Activity: Screens that interact directly with the user.
• Fragment: Modular components running inside Activities.
• Lifecycle: Represents the lifecycle stages of each Activity and Fragment.

Quick Tip: Methods like onCreate(), onResume(), onPause() are frequently asked. Using ViewModel and LiveData with Android Jetpack is also important.

3. Kotlin Coroutines Interview Questions: Asynchronous Programming

What are Coroutines and why use them?

Coroutines are lightweight, efficient asynchronous constructs in Kotlin. Instead of opening threads, suspending functions reduce resource usage. Controlled via functions like launch, async, and withContext.

Code Example:

GlobalScope.launch {
  val data = async { fetchData() }
  println(data.await())
}

Tip: Learn what Dispatchers.IO, Dispatchers.Main do. Structured concurrency is the foundation of Kotlin coroutines.

4. Kotlin Backend Interview Questions

Tools used in Kotlin backend development:

• Ktor: Lightweight Kotlin backend framework.
• Spring Boot: Java’s Spring framework usable with Kotlin.
• Exposed ORM: Kotlin SQL DSL library.

Ktor Route Example:

routing {
  get("/") {
      call.respondText("Hello Kotlin Backend!", ContentType.Text.Plain)
  }
}

5. Kotlin Technical Test: Functions and Lambda Usage

• Functions are first-class citizens and can be assigned to variables.
• Lambda expressions improve code readability, especially on lists with map, filter, forEach.

Example:

val numbers = listOf(1, 2, 3, 4)
val squares = numbers.map { it * it }

6. Kotlin Job Interview Questions: Real-World Scenarios

If your app suddenly slows down, what do you do?

• Use Android Studio Profiler to check CPU and memory consumption.
• Review ANR logs for non-responsive UI issues.
• Check coroutine misuse—heavy work on the main thread causes performance drops.

Tip: Incorrect coroutine usage can cause serious performance problems.

7. Kotlin Object and Companion Object Concepts

How to define a Singleton in Kotlin?

• Use the object keyword for singleton objects.
• companion object defines static members tied to a class.

Example:

object Logger {
  fun log(message: String) {
      println("Log: $message")
  }
}

8. Android Development Interview Questions: MVVM Architecture

• Model: Represents data.
• View: User interface components.
• ViewModel: Acts as a bridge between View and Model.

Tip: LiveData and ViewModel classes can be used with Jetpack Compose. Interviewers may ask about data flow with MVVM.

9. Kotlin Extension Functions

What are extension functions and how are they used?

Kotlin lets you add new functions to existing classes without inheritance.

Example:

fun String.lowercaseCustom(): String = this.lowercase()

val result = "HELLO".lowercaseCustom() // "hello"

10. Kotlin Null Safety Interview Questions

How is null safety achieved in Kotlin?

• Nullable types are declared with ?.
• Use safe calls (?.) and Elvis operator (?:) to handle nulls safely.

Example:

val name: String? = null

val length = name?.length ?: 0 // Returns 0 if null

Kotlin is rapidly rising in modern software development, especially in Android development, backend services, coroutine usage, and syntactic sugar compared to Java. The Kotlin interview questions, Kotlin Android interview questions, Kotlin coroutines interview questions, Kotlin backend interview questions, and Android development interview questions covered here are critical for candidates looking to stand out.

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