Kotlin Interview Questions and Answers

Answer: Defines scope for coroutine lifecycle

CoroutineScope defines coroutine lifecycle. Provides context and manages child coroutines. Use GlobalScope, lifecycleScope, viewModelScope. Structured concurrency.

Answer: Functions taking functions as parameters or returning functions

Higher-order functions take functions as parameters or return functions. Example: fun operate(x: Int, op: (Int) -> Int) = op(x). Foundation of functional programming.

Answer: Modern statically-typed programming language for JVM, Android, JS

Kotlin is a modern, statically-typed programming language developed by JetBrains. It runs on JVM, compiles to JavaScript, and is Google's preferred language for Android development.

Answer: Set of elements defining coroutine behavior

CoroutineContext is indexed set of elements: Job, Dispatcher, CoroutineName, ExceptionHandler. Combine with +. Child inherits parent context.

Answer: Concise syntax, null safety, modern features

Kotlin offers concise syntax (less boilerplate), null safety, extension functions, coroutines, smart casts, and many modern features while maintaining 100% Java interoperability.

Answer: Configures object and returns it

apply executes block on object and returns object: person.apply { name = "John"; age = 30 }. Use for object initialization. this refers to object.

Answer: Executes lambda and returns result

let executes lambda with object as it and returns lambda result: name?.let { println(it.length) }. Good for null checks. it refers to object.

Answer: val (immutable) or var (mutable)

Use val for immutable (read-only) variables: val x = 5. Use var for mutable variables: var y = 10. val is preferred for immutability.

Answer: Determines thread for coroutine execution

Dispatcher determines thread: Dispatchers.Main (UI), IO (blocking IO), Default (CPU-intensive), Unconfined (inherits). Set with withContext or CoroutineScope.

Answer: Switches coroutine context temporarily

withContext switches context for block: withContext(Dispatchers.IO) { readFile() }. Suspends, switches, executes, returns to original. Returns last expression.

Answer: val is immutable, var is mutable

val (value) is read-only, assigned once. var (variable) is mutable, can be reassigned. val x = 5 cannot be changed. var y = 5 can be changed to y = 10.

Answer: Performs action and returns object

also performs action and returns original object: list.also { println("Size: ${it.size}") }. Use for side effects. it refers to object.

Answer: Parent waits for children, propagates cancellation

Structured concurrency ensures parent waits for children. Canceling parent cancels children. Exceptions propagate. Prevents coroutine leaks. Foundation of Kotlin coroutines.

Answer: fun functionName(params): ReturnType

Use fun keyword: fun add(a: Int, b: Int): Int { return a + b }. Single-expression functions: fun add(a: Int, b: Int) = a + b.

Answer: Executes block and returns result

run executes block and returns result: val result = person.run { "$name is $age" }. Use for computing value. this refers to object.

Answer: Cancellable thing with lifecycle

Job represents coroutine lifecycle. Returned by launch. States: New, Active, Completing, Completed, Cancelling, Cancelled. Cancel: job.cancel(). Join: job.join().

Answer: Compiler automatically determines type

Type inference allows compiler to deduce types: val x = 5 (Int inferred). Makes code more concise while maintaining type safety.

Answer: Calls block with receiver as this

with is non-extension function taking receiver: with(person) { println(name) }. Returns lambda result. Use for multiple operations on object. this refers to receiver.

Answer: Restricted class hierarchy with known subclasses

Sealed class restricts inheritance: sealed class Result. Subclasses must be in same file. Great with when for exhaustive handling. Represents restricted alternatives.

Answer: Job where child failure doesn't affect siblings

SupervisorJob: child failure doesn't cancel parent or siblings. Regular Job: any child failure cancels all. Use for independent operations that shouldn't affect each other.

Answer: Type system distinguishes nullable and non-nullable types

Null safety prevents NullPointerException. Types are non-nullable by default. Use ? for nullable: String? can be null, String cannot. Compile-time null safety.

Answer: Add ? after type: String?

Append ? to type for nullable: var name: String? = null. Without ?, variable cannot be null: var name: String = "John" (cannot assign null).

Answer: Asynchronous stream of values

Flow is cold asynchronous stream: flow { emit(1); emit(2) }. Suspending, cancellable. Terminal operators: collect, first, reduce. Operators: map, filter, transform.

Answer: Unpacks object into multiple variables

Destructuring unpacks objects: val (name, age) = person. Works with data classes, Pair, List. Uses componentN() functions. Max 5 components without custom implementation.