Kotlin : 100 Interview Questions and Answers PART 1

1. What is kotlin ?

Kotlin is a modern, statically typed programming language that runs on the Java Virtual Machine (JVM) and can also be compiled to JavaScript, native code, and even used for Android development, web, desktop, and server-side applications.

Key Features of Kotlin:

2. Where Koltin is used ?

a. Android App Development – Officially supported by Google since 2017.

• b. Backend Development – With frameworks like Spring Boot or Ktor.
• c. Desktop Applications – Using libraries like TornadoFX or Compose Multiplatform.
• d. Scripting and CLI Tools – Kotlin scripts are clean and effective.
• e. Web Development – Kotlin/JS can compile Kotlin to JavaScript.
• f. Multiplatform Development – Share business logic between iOS, Android, and web.

3.  How is Kotlin different from Java ?

Kotlin and Java are both powerful languages that run on the Java Virtual Machine (JVM), but Kotlin was designed to fix some of Java’s shortcomings and make development more concise, safe, and modern.

4. Benefits of using Kotlin ?

Here’s a comprehensive list of Kotlin’s features that make it a modern, powerful, and developer-friendly language:

🚀 Core Features of Kotlin

✅ 1. Concise Syntax

• -Reduces boilerplate code.
• -Easier to write and read than Java.

✅ 2. Null Safety

• Eliminates NullPointerException at compile time using nullable (?) and non-nullable types.

val name: String? = null 
println(name?.length)  // Safe call 

✅ 3. Interoperable with Java

• 100% compatible with existing Java libraries, frameworks, and projects.
• You can call Java code from Kotlin and vice versa.

✅ 4. Smart Casts

• Automatically casts types after a type-check.

if (obj is String) {    
  println(obj.length) // smart cast to String 
}

✅ 5. Extension Functions

• Add new functions to existing classes without inheritance or modifying the class.

fun String.capitalizeFirst(): String = this.replaceFirstChar { it.uppercase() }

✅ 6. Coroutines for Asynchronous Programming

• Lightweight threads to write non-blocking, asynchronous code simply and efficiently.

launch {    
	val data = fetchData()    
	println(data) 
}

✅ 7. Data Classes

• Automatically generates useful methods: equals(), hashCode(), toString(), copy().

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

✅ 8. Default and Named Arguments

• Avoid method overloading by using default values and named parameters.

fun greet(name: String = "Guest", age: Int = 0) 
greet(age = 25)

✅ 9. Sealed Classes

• Represent restricted class hierarchies (like enums, but more powerful).

sealed class Result 
data class Success(val data: String): Result() 
object Error: Result()

✅ 10. Type Inference

• Automatically infers variable types, reducing verbosity.

val name = "Bind the Logic"  // Inferred as String 

✅ 11. Functional Programming Support

• High-order functions, lambdas, immutability.

val list = listOf(1, 2, 3).map { it * 2 }

✅ 12. Destructuring Declarations

• Unpack multiple properties from data classes or collections.

val (name, age) = User("Alice", 30)

✅ 13. Companion Objects

• Acts like static members in Java.

class MyClass {    
	companion object {        
		fun create(): MyClass = MyClass()    
	} 
}

✅ 14. Scripting Support

• Kotlin can be used for scripting (e.g., .kts files) for automation or lightweight tasks.

✅ 15. Multiplatform Development

• Write shared code for JVM, Android, iOS, web (via Kotlin/JS), desktop, and embedded systems.

5. Basic data types in kotlin .

Here's a table of basic data types in Kotlin along with their descriptions and example usage:

6. Difference between val and var keyword.

In Kotlin, val and var are both used to declare variables, but they have different behaviors regarding mutability:

val vs var in Kotlin