Kotlin Exercises with Answers
Practise Kotlin with 143 interactive exercises: multiple choice, fill-in-the-blank, output prediction and debugging. Every exercise gives instant feedback, a hint and the full solution.
Topic All topics Introduction Variables & Types Numbers & Operators Strings Null Safety if & when Loops & Ranges Functions Lists Maps & Sets Collection Operations Lambdas Classes & Objects Data Classes Inheritance & Interfaces Objects & Companions Enums & Sealed Classes Exceptions Extension Functions Generics Scope Functions Coroutines Flows Files & I/O Testing Arrays and primitive arrays Packages and visibility Type checks and casts Delegated properties Interface delegation Nested and inner classes Inline functions and returns Operator overloading Sequences Equality and hashing Regex parsing Java interoperability Gradle Kotlin DSL JSON serialization Dates and time zones Supervision and cleanup Shared state and Mutex Flow buffering and sharing All types Fill in the blanks Predict the output Multiple choice
Any level Easy Medium Hard
Score 0 / 143
fun main ( ) {
print ( "A" )
print ( "B" )
println ( "C" )
} A ABC B A, B and C on separate lines C A B C D CBA
print doesn't add a new line, so all three letters appear together.
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fun main ( ) {
println ( "2 + 2" )
println ( 2 + 2 )
} A 4 and 4 B 2 + 2 twice C 2 + 2, then 4 D An error
Quoted text is printed as written; the unquoted sum is calculated.
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Which file extension do Kotlin source files use?
A .kotlin B .kts only C .java D .kt
.kts is for Kotlin scripts, such as Gradle build files; normal source files use .kt.
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Why can Kotlin programs use Java libraries?
A Kotlin is a newer name for Java B Kotlin compiles to JVM bytecode, the same format Java uses C Kotlin converts Java code to Kotlin automatically D It can't
Both run on the Java Virtual Machine, so they work together.
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Complete the code so count can be changed later.
= 0
count = 5
var allows reassignment; val doesn't.
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What type does Kotlin infer for val x = 4.0?
A Int B Double C Float D String
A number with a decimal point is a Double by default.
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var a = 5
val b = a
a = 9
println ( b) A 5 B 9 C 14 D An error
b got the value 5 when it was created; changing a later doesn't affect it.
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Which line converts "7" into a number safely, without crashing on bad text?
A "7".toInt() B Int("7") C (Int) "7" D "7".toIntOrNull()
toIntOrNull returns null for invalid text.
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Where can const val be declared?
A Inside any function B Only inside main C At the top level of a file, or inside an object D Anywhere a var can go
const values must be known at compile time and can't be local variables.
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Complete the code so it prints the remainder of 17 divided by 5.
println ( 17 5 )
% gives the remainder: 2.
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What does println(9 / 2) print?
A 4.5 B 5 C 4 D 4.0
Both values are Ints, so the decimals are dropped.
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var x = 10
x -= 3
x *= 2
println ( x) A 17 B 20 C 7 D 14
10 minus 3 is 7, and 7 times 2 is 14.
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Which expression is true only when age is from 13 to 19?
A age >= 13 && age <= 19 B age > 13 || age < 19 C age >= 13 || age <= 19 D !(age == 13)
&& requires both conditions to be true.
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How do you show 2.5 as "2.50"?
A 2.5.toString(2) B round(2.5, 2) C "%.2f".format(2.5) D 2.5.toInt()
The format string %.2f always shows two decimal places.
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Complete the template so it prints "Hello, Ada".
val name = "Ada"
println ( "Hello, ")
$name inserts the variable's value into the string.
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What does println("Kotlin".length) print?
A 5 B 7 C 6 D Kotlin
K-o-t-l-i-n is six characters.
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val s = "banana"
println ( s. substring ( 1 , 4 ) ) A ban B anan C ana D nan
Indexes 1, 2 and 3: a, n, a. The end index isn't included.
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Which line prints "Total: 15"?
A println("Total: $a + $b") with a = 10, b = 5 B println("Total: " + a + b) with a = 10, b = 5 C println('Total: ${a + b}') D println("Total: ${a + b}") with a = 10, b = 5
The expression must be inside ${ } to be calculated.
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val parts = "a-b-c" . split ( "-" )
println ( parts. joinToString ( "" ) ) A abc B a-b-c C [a, b, c] D a b c
split removes the dashes, and joining with an empty separator puts the letters together.
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Complete the declaration so middleName can be null.
var middleName: String = null
Adding ? makes the type nullable.
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val city: String ? = null
println ( city ? : "Unknown" ) A null B An empty line C Unknown D An error
Elvis uses the right side when the left side is null.
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val word: String ? = "kotlin"
println ( word? . uppercase ( ) ? . length ) A KOTLIN B null C An error D 6
word isn't null, so both safe calls run and give the length 6.
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What does s?.let { println(it) } do when s is null?
A Nothing: the block doesn't run B Prints null C Throws an exception D Prints an empty line
The safe call skips let entirely for null.
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Why is !! usually a warning sign in code reviews?
A It's slow B It crashes with a NullPointerException if the value is null, undoing Kotlin's protection C It only works on Strings D It makes the variable immutable
Prefer safe calls, Elvis, if checks or let.
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Complete the expression so it returns "Even" or "Odd".
val kind = if ( n % 2 == 0 ) "Even" "Odd"
An if expression needs an else branch.
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val x = 7
when ( x) {
1 , 3 , 5 , 7 , 9 -> println ( "odd" )
else -> println ( "even" )
} A odd B even C 7 D Nothing
7 matches one of the listed values.
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val temp = 18
val advice = when {
temp > 25 -> "hot"
temp > 15 -> "mild"
temp > 5 -> "cool"
else -> "cold"
}
println ( advice) A hot B mild C mild and cool D cool
Only the first true branch runs.
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Which when branch matches every number from 10 to 20?
A 10 - 20 -> B 10, 20 -> C is 10..20 -> D in 10..20 ->
in checks membership in a range.
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What value does this block produce?
val result = if ( true ) {
println ( "checking" )
42
} else {
0
} A "checking" B 42 C Unit D 0
The last expression in the chosen block is its value.
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Complete the loop so it prints 10, 9, 8 ... 1.
for ( i in 10 1 ) println ( i)
downTo creates a range that counts down.
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How many numbers does for (i in 0 until 4) loop over?
A 5 B 3 C 4 D 0
0, 1, 2 and 3; until excludes 4.
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for ( i in 1 . . 10 step 3 ) print ( "$i " ) A 1 3 6 9 B 3 6 9 C 1 4 7 D 1 4 7 10
Start at 1 and add 3 each time; 10 is included.
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Which loop always runs its body at least once?
A for B while C do-while D repeat(0)
do-while checks its condition after the body.
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var total = 0
for ( n in 1 . . 6 ) {
if ( n == 4 ) continue
total += n
}
println ( total) A 21 B 6 C 10 D 17
1 + 2 + 3 + 5 + 6 = 17; 4 is skipped.
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Complete the function so it returns the square of n.
square ( n: Int ) : Int = n * n
fun declares a function; = gives a single-expression body.
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fun greet ( name: String = "friend" ) = "Hi, $name"
println ( greet ( ) ) A Hi, B Hi, name C An error D Hi, friend
The default value is used when no argument is given.
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fun box ( w: Int = 1 , h: Int = 1 ) = w * h
println ( box ( h = 5 ) ) A 1 B 6 C An error D 5
w keeps its default of 1, and h is 5.
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What is the return type of a function that only prints?
A Void B Nothing C Unit D Null
Unit means "no useful value" and can be left out.
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Which call is valid for fun send(to: String, subject: String = "Hi", urgent: Boolean = false)?
A send("sam@example.com", urgent = true) B send(urgent = true) C send("sam@example.com", true) D send(subject = "Hi", "sam@example.com")
to has no default and must be given; the named argument skips subject.
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easy Lists Complete the code so the list can have items added.
val cart = ( "bread" )
cart. add ( "eggs" )
mutableListOf creates a list that can change.
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easy Lists val xs = listOf ( "a" , "b" , "c" , "d" )
println ( xs[ 2 ] ) A c B b C d D An error
Indexes start at 0, so index 2 is the third item.
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medium Lists val xs = mutableListOf ( 5 , 3 , 8 )
xs. add ( 0 , 1 )
xs. removeAt ( 2 )
println ( xs) A [1, 5, 3] B [5, 3, 8, 1] C [1, 3, 8] D [1, 5, 8]
After adding at 0 the list is [1, 5, 3, 8]; removing index 2 removes the 3.
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medium Lists What's the difference between sort() and sorted()?
A sort is faster B sorted only works on numbers C sort changes a mutable list in place; sorted returns a new list D There's none
The -ed versions leave the original untouched.
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Why can val basket = mutableListOf<String>() still have items added?
A val doesn't work with lists B val stops the variable pointing to a different list, but the mutable list's contents can change C It's a bug D Lists are always mutable
val is about the reference, not the contents.
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Complete the line so it sets the price of juice to 1.9.
prices[ " "] = 1.9
map[key] = value adds or updates an entry.
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val m = mapOf ( "a" to 1 , "b" to 2 )
println ( m[ "c" ] ) A null B 0 C An exception D c
Missing keys return null.
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val s = mutableSetOf ( 1 , 2 , 3 )
s. add ( 2 )
s. add ( 4 )
println ( s. size ) A 5 B 4 C 3 D 2
2 is already there, so only 4 is added.
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Which expression gives every item in set a that isn't in set b?
A a union b B a intersect b C a subtract b D b subtract a
subtract removes b's items from a.
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val counts = mutableMapOf < Char , Int > ( )
for ( c in "banana" ) counts[ c] = ( counts[ c] ? : 0 ) + 1
println ( counts) A {b=1, a=1, n=1} B {a=3, n=2, b=1} C {b=1, a=3, n=2} D [b, a, n]
Each letter is counted, in the order it first appears.
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Complete the code so it keeps only numbers greater than 10.
val big = numbers. { it > 10 }
filter keeps items for which the block returns true.
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println ( listOf ( 1 , 2 , 3 ) . map { it * it } ) A [2, 4, 6] B 14 C [1, 2, 3] D [1, 4, 9]
map squares each number.
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val words = listOf ( "apple" , "kiwi" , "banana" , "fig" )
println ( words. filter { it. length > 3 } . map { it. uppercase ( ) } ) A [APPLE, KIWI, BANANA] B [APPLE, KIWI, BANANA, FIG] C [APPLE, BANANA] D [apple, kiwi, banana]
fig is filtered out; the rest are uppercased.
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Which returns a Map from each category to its products?
A products.associate { it.category } B products.groupBy { it.category } C products.partition { it.category } D products.map { it.category }
groupBy collects items with the same key into lists.
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val ( even, odd) = ( 1 . . 6 ) . partition { it % 2 == 0 }
println ( even. sum ( ) - odd. sum ( ) ) A 0 B -3 C 3 D 21
2 + 4 + 6 is 12 and 1 + 3 + 5 is 9.
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Complete the lambda so it returns its number plus one.
val inc: ( Int ) -> Int = { + 1 }
it is the implicit name of a single parameter.
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val f = { x: Int -> x * 3 }
println ( f ( 4 ) ) A 7 B 12 C 43 D An error
The lambda multiplies its argument by 3.
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fun applyTwice ( x: Int , f: ( Int ) -> Int ) = f ( f ( x) )
println ( applyTwice ( 2 ) { it * 5 } ) A 10 B 25 C 50 D 7
2 times 5 is 10, then 10 times 5 is 50.
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What does the type (String) -> Boolean describe?
A A String that may be a Boolean B A function that takes a String and returns a Boolean C A Boolean variable named String D A list of Strings
Inputs are in brackets, the output after the arrow.
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fun adder ( n: Int ) : ( Int ) -> Int = { it + n }
val add5 = adder ( 5 )
val add10 = adder ( 10 )
println ( add5 ( 1 ) + add10 ( 1 ) ) A 17 B 12 C 16 D 2
6 plus 11; each lambda remembers its own n.
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Complete the constructor so name becomes a read-only property.
class City ( : String )
val in the constructor creates a read-only property.
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class Counter ( var n: Int = 0 ) {
fun up ( ) { n++ }
}
val c = Counter ( 5 )
c. up ( ) ; c. up ( )
println ( c. n ) A 7 B 5 C 2 D 0
It starts at 5 and is increased twice.
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What does private set on a property do?
A Hides the property completely B Makes it a constant C Deletes the setter D Lets anyone read it but only the class change it
The getter stays public.
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Where should you check that constructor values are valid?
A In main B In an init block, with require C In a getter D In toString
init runs every time an object is created.
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class Box ( val w: Int , val h: Int ) {
val area get ( ) = w * h
}
val b = Box ( 3 , 4 )
println ( b. area + Box ( 2 , 2 ) . area ) A 7 B 12 C 16 D 11
12 plus 4.
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Complete the declaration so Point gets a generated toString and equals.
class Point ( val x: Int , val y: Int )
The data keyword generates the useful functions.
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data class Pet ( val name: String , val age: Int )
println ( Pet ( "Rex" , 3 ) ) A Pet@1b6d3586 B Rex 3 C Pet(name=Rex, age=3) D {name=Rex, age=3}
The generated toString lists the properties.
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data class Size ( val w: Int , val h: Int )
val a = Size ( 2 , 3 )
val b = a. copy ( h = 9 )
println ( "${a.h} ${b.h}" ) A 9 9 B 3 3 C An error D 3 9
copy creates a new object; a is unchanged.
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Which properties does a data class use for equals and toString?
A Only the properties declared in the primary constructor B All properties in the class C Only var properties D Only the first property
Properties in the class body are ignored.
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Which is the best fit for a regular class rather than a data class?
A A Point with x and y B A Money value with an amount and currency C A BankAccount whose balance changes and which has its own identity D A User loaded from an API
Two accounts with equal balances are still different accounts.
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Complete the class so other classes can inherit from it.
class Vehicle ( val wheels: Int )
Classes are final unless marked open.
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How many classes can a Kotlin class extend?
A One B Two C Unlimited D None
A class can extend one class but implement many interfaces.
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open class A { open fun hi ( ) = "A" }
class B : A ( ) { override fun hi ( ) = "B" + super . hi ( ) }
println ( B ( ) . hi ( ) ) A A B B C BA D AB
B's version adds "B" before the parent's result.
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What must a subclass of an abstract class do?
A Nothing special B Provide an implementation for every abstract member C Mark itself abstract D Call super in every method
Otherwise it must be abstract too.
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Why does Kotlin make classes final by default?
A To save memory B To prevent fragile, accidental inheritance; you opt in with open when a class is designed for it C Because Kotlin doesn't support inheritance D To make classes faster to create
It encourages interfaces and composition.
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Complete the declaration so Config is a singleton.
Config {
val apiUrl = "https://api.example.com"
}
object declares a class with exactly one instance.
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How do you call create in a companion object of class User?
A User().create() B companion.create() C new User.create() D User.create()
Companion members are called on the class name.
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object Counter { var n = 0 }
Counter . n ++
Counter . n += 5
println ( Counter . n ) A 6 B 0 C 5 D 1
There's one shared instance, so both changes apply to the same n.
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Why combine a private constructor with a companion factory function?
A To make objects faster B So every object is created through the factory, which can validate or return null C To allow inheritance D To make the class a singleton
Outside code can't bypass the checks.
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When is a top-level function better than an object holding the function?
A Never B When you need a singleton C When implementing an interface D For a simple utility with no shared state, like formatting a price
Kotlin allows functions outside classes.
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Complete the declaration of an enum for directions.
class Direction { NORTH, EAST, SOUTH, WEST }
enum class defines a fixed set of constants.
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enum class Size { S, M, L }
println ( Size . L . ordinal ) A 2 B 3 C L D 1
ordinal counts from 0.
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When should you use a sealed class instead of an enum?
A When each case carries different data, such as Success(items) and Error(message) B When there are more than three options C When you need a String value D Never
Enum constants all share the same shape.
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Why can a when over a sealed interface skip else?
A else is never allowed B The compiler knows every possible subtype, so it can check all are handled C Sealed types can't be null D It only works with one case
That's what makes it exhaustive.
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enum class Op ( val f: ( Int , Int ) -> Int ) {
ADD ( { a, b -> a + b } ) , MUL ( { a, b -> a * b } )
}
println ( Op . entries . map { it. f ( 3 , 4 ) } ) A [7, 7] B [ADD, MUL] C [12, 7] D [7, 12]
Each constant stores its own function.
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Complete the code so the clean-up message always prints.
try {
work ( )
} catch ( e: Exception ) {
println ( "Failed" )
} {
println ( "Cleaned up" )
}
finally runs whether or not an exception happened.
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val x = try { "5" . toInt ( ) } catch ( e: Exception ) { - 1 }
println ( x) A -1 B "5" C An error D 5
Parsing succeeds, so the try block's value is used.
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Which exception does require(false) { "bad" } throw?
A IllegalArgumentException B IllegalStateException C NullPointerException D NumberFormatException
require is for checking arguments; check throws IllegalStateException.
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val r = runCatching { listOf ( 1 , 2 ) [ 5 ] }
println ( r. getOrElse { 0 } ) A 2 B null C 0 D An IndexOutOfBoundsException
runCatching captures the exception and getOrElse supplies 0.
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Does Kotlin force you to catch exceptions that a function might throw?
A Yes, like Java's checked exceptions B No, Kotlin has no checked exceptions C Only for IOException D Only in main
It's your responsibility to handle the ones that matter.
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Complete the extension so it can be called as "hi".shout().
fun . shout ( ) = uppercase ( ) + "!"
The receiver type goes before the function name.
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fun Int . isEven ( ) = this % 2 == 0
println ( 7 . isEven ( ) ) A true B 7 C false D An error
this is 7, which isn't even.
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val String . lastChar : Char get ( ) = this [ length - 1 ]
println ( "Kotlin" . lastChar ) A K B n C 6 D An error
The extension property returns the final character.
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Can an extension function read a class's private properties?
A Yes, always B Only for data classes C Only if it's infix D No, only its public members
Extensions don't break encapsulation.
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A class has a member fun greet() and there's also an extension fun MyClass.greet(). Which runs for obj.greet()?
A The extension B The member function C Both D It doesn't compile
Members always win over extensions with the same signature.
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Complete the declaration of a generic class that holds one item of any type.
class Box < > ( val item: T)
T is the conventional name for a type parameter.
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Where does a generic function declare its type parameter?
A After the parameters B Before the function name, as in fun <T> f(x: T) C In the return type only D It doesn't need one
fun <T> comes first.
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fun < T> twice ( x: T) : List < T> = listOf ( x, x)
println ( twice ( "ha" ) ) A [ha, ha] B haha C [ha] D An error
T is inferred as String and a list of two items is returned.
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What does T : Comparable<T> mean?
A T must be exactly Comparable B T is optional C T can be any type that can be compared with itself D T must be a number
It's an upper bound.
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Why can a List<Cat> be passed where List<Animal> is expected, but not a MutableList<Cat> for MutableList<Animal>?
A Lists are faster B MutableList isn't generic C List only produces items (out), so it's safe; a MutableList could have a Dog added to it D It's a compiler bug
Producer out, consumer in.
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Complete the code so the block runs only when name isn't null.
name? . { println ( "Hi, $it" ) }
?.let runs the block with it as the non-null value.
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Which scope function returns the object itself and refers to it as this?
A apply B let C also D run
apply is ideal for configuring an object.
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val n = 5 . let { it * 2 } . also { println ( "got $it" ) }
println ( n) A got 5, then 5 B got 10, then 10 C 10 only D got 10, then 5
let returns 10; also prints it and passes 10 on.
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val x = "abc" . takeIf { it. length > 5 } ? : "short"
println ( x) A abc B null C true D short
takeIf returns null when the condition is false, so Elvis gives "short".
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Which is the best choice for logging a value in the middle of a chain without changing it?
A also B let C run D with
also passes the original object on.
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Complete the declaration so the function can call delay.
fun loadData ( ) : String {
delay ( 500 )
return "data"
}
Only suspend functions (or coroutines) can call delay.
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Which builder returns a result you can await?
A launch B runBlocking C async D delay
async returns a Deferred; launch returns a Job.
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fun main ( ) = runBlocking {
launch { delay ( 50 ) ; print ( "B" ) }
print ( "A" )
} A BA B A only C B only D AB
The launched coroutine suspends at delay, so A prints first; runBlocking waits for B.
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Which dispatcher suits reading a large file?
A Dispatchers.IO B Dispatchers.Main C Dispatchers.Unconfined D No dispatcher
IO is for network and disk work.
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Two async calls each take one second. When does awaiting both take about one second in total?
A Never B When they use Thread.sleep C When they're inside separate runBlocking calls D When both async blocks are started before either is awaited
Starting both first lets them overlap.
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easy Flows Complete the flow builder so it sends the value 42 to collectors.
val f = flow {
( 42 )
}
emit sends a value from inside the flow builder.
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When does the code inside flow { } run?
A As soon as the flow is created B Only once ever C On a background thread automatically D When it's collected, separately for each collector
Flows are cold.
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medium Flows runBlocking {
flowOf ( 1 , 2 , 3 , 4 ) . filter { it % 2 == 0 } . map { it * 10 } . collect { print ( "$it " ) }
} A 20 40 B 10 20 30 40 C 2 4 D 10 30
The even numbers 2 and 4 are kept and multiplied by 10.
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medium Flows What's the key difference between StateFlow and a normal Flow?
A StateFlow is faster B StateFlow is hot and always has a current value that new collectors receive immediately C StateFlow can't be collected D StateFlow only holds Strings
Normal flows are cold and have no current value.
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Which operator should a search box use so it only searches after the user stops typing for a moment?
A take B zip C reduce D debounce
debounce waits for a pause between values.
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Complete the line that adds text to the end of a file.
File ( "log.txt" ) . ( "Saved\n" )
appendText adds to the end instead of replacing the file.
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What does File("a.txt").writeText("hi") do to an existing file?
A Adds hi to the end B Nothing C Throws an exception D Replaces its contents with hi
Use appendText to add instead.
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Which is best for counting lines in a 5 GB file?
A readText() B useLines { it.count() } C readLines() D readBytes()
useLines processes one line at a time.
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What does use { } guarantee?
A The resource is closed when the block ends, even if an exception happens B The file is read faster C The file is created if missing D Errors are ignored
It's Kotlin's try-with-resources.
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A file contains "a\nb\nc\n". What does readLines().size return?
A 4 B 1 C 3 D 6
The trailing newline doesn't produce an extra empty line.
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Complete the annotation that marks a function as a test.
fun `adds two numbers`( ) {
assertEquals ( 4 , 2 + 2 )
}
@Test tells the test runner to run the function.
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In assertEquals(a, b), which is the expected value?
A a, the first argument B b, the second argument C Either D Neither
Expected first, actual second.
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How do you check that a call throws IllegalArgumentException?
A assertEquals(IllegalArgumentException, call()) B assertFailsWith<IllegalArgumentException> { call() } C try { call() } catch (e: Exception) { } D @Test(expected = Exception)
assertFailsWith also returns the exception for further checks.
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Why use a fake repository in tests?
A Fakes are required by kotlin.test B It makes the app faster C It hides bugs D It gives fast, predictable data without a real database or network
Tests stay quick and reliable.
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What does runTest do with delay(5_000)?
A Skips it using virtual time, so the test finishes almost instantly B Waits five real seconds C Throws an exception D Runs it on a background thread
That's why runTest is used for coroutine tests.
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A matrix must have independent mutable rows. Which initializer fits?
A Create one IntArray and put that same instance in every row B Use one integer variable for the entire matrix C Array(3) { IntArray(2) }
The initializer creates a separate row array for each outer position, avoiding accidental shared-row updates.
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A count should be readable publicly but writable only by its class. Which design fits?
A A public mutable field with no checks B A private class whose state is never read C A public property with private set and checked mutation methods
Restricting the setter preserves observation while making the permitted changes explicit.
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An unknown value must be a list containing only strings. Which plan is appropriate?
A Check List<*> and validate each element B Assume List<*> guarantees string elements C Cast to List<String> without examining input
The outer list shape and the element contract need separate validation because generic arguments are erased.
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A service is required for every valid instance and is available at construction. Which approach is usually clearest?
A Leave it lateinit and hope a caller assigns it B Hide its absence behind a lazy fallback C Require it as a constructor dependency
Constructor injection establishes the required dependency when the object becomes usable.
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A wrapper must validate one operation before forwarding. Which implementation fits?
A Trust that overriding an unrelated property secures every call B Override the exposed operation and call a private delegate after validation C Expose the delegate publicly so callers can bypass checks
The policy belongs on the actual public operation being controlled.
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A receipt label must never change after purchase. Which model best expresses that requirement?
A An inner helper reading the current mutable catalog title B A global variable updated on every catalog rename C A separate value storing the approved title snapshot
Historical output should use a stable captured value rather than a live owner relationship.
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A lambda is invoked through a nested Runnable and must not return from its caller. Which modifier expresses that restriction?
A reified on the lambda variable B inner C crossinline
Crossinline forbids non-local returns while preserving the parameter's inlining eligibility.
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A business operation sends a payment and can fail in several ways. What API is usually clearer?
A Hide payment behind an unrelated plus operator B Use get() merely because brackets are short C A named payment method with an explicit result contract
A clear verb and failure contract communicate substantial side effects better than surprising symbolic syntax.
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A sequence may be infinite. Which expression obtains a bounded sample?
A values.take(5).toList() B values.toList().take(5) C values.count()
take must bound consumption before the terminal operation attempts to materialize the source.
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Which design best supports changing a customer's display name?
A A mutable display name used directly as the identity key. B A data class key with a mutable equality-relevant id changed after insertion. C An immutable customer-id key with display name stored in the value.
Keep equality-relevant key state stable while editable profile details change independently.
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A captured digit string must represent an Int from 1 through 100. Which approach handles both limits?
A Use find anywhere in the text and accept the first digits. B Convert with toIntOrNull, then check the resulting value in 1..100. C Check that every character is a digit and assume conversion succeeds.
Numeric representability and the business range are separate from the text's digit shape.
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Main.kt now declares package shop. Which entry point matches its top-level main?
A stock-demo B shop.Main C shop.MainKt
The package qualifies the generated file-facade class MainKt used by this example.
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A nullable field should accept omission as null. Which declaration states that ordinary policy?
A val note: String? B val note: String? = null C val note: String
An explicit default handles absence; nullability alone handles a null value, not necessarily a missing key.
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Which design makes a due-date test independent of the machine's current day?
A Pass a fixed Clock with an explicit business zone. B Call LocalDate.now() inside the assertion with the default zone. C Sleep until midnight before running the test.
A supplied fixed clock makes both the moment and local calendar interpretation deterministic.
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Where should a necessary bounded suspending cleanup run after cancellation?
A In GlobalScope with no owner. B Around the whole operation forever using NonCancellable. C In finally, using a narrow withContext(NonCancellable) region if needed.
This pattern preserves structured ownership while allowing required cleanup to complete.
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Which statement accurately describes an in-process Mutex?
A It protects callers that ignore the mutex as strongly as callers that acquire it. B It coordinates cooperating access to local shared state through that mutex. C It automatically locks the same database row in every server process.
External persistence and noncooperating access require their own consistency boundaries.
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A temporary component shares an expensive source. Which design addresses its lifetime?
A Use an explicit owner scope and an appropriate SharingStarted policy. B Create a detached scope and never retain or cancel it. C Assume replay size automatically closes the source.
The scope owns collection lifetime, while the starting policy controls subscriber-driven behavior.
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