Top Basic Kotlin Interview Questions and Answers for TCS

Introduction

Preparing for a Kotlin interview at TCS? Kotlin has become a preferred language for Android development, backend services, and cross-platform applications. TCS frequently asks fundamental Kotlin questions to evaluate a candidate’s knowledge of the language.

This blog provides a comprehensive list of basic Kotlin interview questions to help freshers and experienced professionals succeed in their TCS technical interview.

✔ Covers essential Kotlin concepts
✔ Includes real-world examples
✔ Ideal for freshers and experienced developers

📌 Bookmark this page and review these questions before your TCS interview! 🚀

Top Basic Kotlin Interview Questions and Answers

1. What is Kotlin?

Answer: Kotlin is a modern, statically typed programming language developed by JetBrains. It is interoperable with Java and widely used for Android, web, and backend development.

2. What are the key features of Kotlin?

Answer:

• Concise – Reduces boilerplate code
• Null Safety – Prevents NullPointerException
• Interoperability – Works seamlessly with Java
• Coroutines – Simplifies asynchronous programming
• Smart Casts – Automatic type conversion
• Extension Functions – Adds functions to existing classes

3. What is the difference between var and val?

Answer:

• var – Mutable (value can be changed)
• val – Immutable (like final in Java)

Example:

var age = 25
age = 30  // Allowed

val name = "TCS"
// name = "Other"  // Error

4. What is type inference in Kotlin?

Answer: Kotlin can automatically infer the data type of variables, eliminating the need for explicit declarations.

Example:

val language = "Kotlin"  // Automatically inferred as String
val number = 10  // Inferred as Int

5. How does Kotlin handle null safety?

Answer: Kotlin prevents NullPointerException by not allowing null values unless explicitly declared as nullable.

Example:

var name: String? = null  // Nullable variable
println(name?.length)  // Safe call operator

6. What is the Elvis operator (?:) in Kotlin?

Answer: The Elvis operator provides a default value if a nullable expression is null.

Example:

val name: String? = null
val length = name?.length ?: 0  // If name is null, return 0
println(length)  // Output: 0

7. What is a when expression in Kotlin?

Answer: when is an enhanced version of Java’s switch statement.

Example:

val number = 3
val result = when (number) {
    1 -> "One"
    2 -> "Two"
    3 -> "Three"
    else -> "Unknown"
}
println(result)  // Output: Three

8. How do you define a function in Kotlin?

Answer: Functions are declared using the fun keyword.

Example:

fun greet(name: String): String {
    return "Hello, $name!"
}
println(greet("TCS"))  // Output: Hello, TCS!

9. What is a default parameter in Kotlin?

Answer: Kotlin allows functions to have default values for parameters.

Example:

fun greet(name: String = "Guest") {
    println("Hello, $name!")
}

greet()  // Output: Hello, Guest!
greet("TCS")  // Output: Hello, TCS!

10. What is the difference between == and === in Kotlin?

Answer:

• == – Compares values (like .equals() in Java)
• === – Compares object references

Example:

val a = "Kotlin"
val b = "Kotlin"
println(a == b)  // true (values are equal)
println(a === b)  // true (same object reference)

11. How do you declare a class in Kotlin?

Answer:

class Person(val name: String, val age: Int)

Example:

val person = Person("John", 25)
println(person.name)  // Output: John

12. What is a data class in Kotlin?

Answer: A data class is used to store data and automatically generates equals(), hashCode(), and toString().

Example:

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

val user = User("Alice", 30)
println(user)  // Output: User(name=Alice, age=30)

13. What are extension functions in Kotlin?

Answer: Extension functions allow adding functions to existing classes without modifying them.

Example:

fun String.addExclamation(): String {
    return this + "!"
}

println("Hello".addExclamation())  // Output: Hello!

14. What is a Singleton in Kotlin?

Answer: A singleton is created using the object keyword.

Example:

object Database {
    val name = "MyDatabase"
    fun connect() = println("Connected to $name")
}

Database.connect()  // Output: Connected to MyDatabase

15. What is the difference between apply, let, run, and with?

Example:

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

val person = Person("Alice", 25).apply {
    age = 30
}
println(person.age)  // Output: 30

16. What is the difference between lazy and lateinit?

Answer:

• lazy – Used for immutable properties (initialized only when accessed).
• lateinit – Used for mutable properties (initialized later).

Example:

val message: String by lazy {
    "Hello, TCS!"
}
println(message)  // Initialized and printed when accessed

17. What is sealed class in Kotlin?

Answer: A sealed class restricts inheritance to a fixed set of subclasses.

Example:

sealed class Result {
    class Success(val data: String) : Result()
    class Error(val message: String) : Result()
}

18. What is Kotlin Coroutines?

Answer: Coroutines are used for asynchronous programming without blocking threads.

Example:

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        println("Hello from Coroutine!")
    }
}

19. What is the use of super keyword in Kotlin?

Answer: The super keyword is used to refer to the parent class’s properties and methods.

Example:

open class Parent {
    open fun show() {
        println("Parent class")
    }
}

class Child : Parent() {
    override fun show() {
        super.show()
        println("Child class")
    }
}

20. What is the difference between first() and find() in Kotlin?

Answer:

• first() – Returns the first element, throws an exception if empty.
• find() – Returns the first matching element, returns null if no match is found.