Kotlin

Q1. You would like to print each score on its own line with its cardinal position. Without using var or val, which method allows iteration with both the value and its position?

fun main() {
  val highScores = listOf(4000, 2000, 10200, 12000, 9030)
}

.withIndex()
.forEachIndexed()
.forEach()
.forIndexes()

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Q2. When the Airplane class is instantiated, it displays Aircraft = null, not Aircraft = C130 why?

abstract class Aircraft {
  init { println("Aircraft = ${getName()}") }
  abstract fun getName(): String
}
class Airplane(private val name: String) : Aircraft() {
  override fun getName(): String = name
}

Classes are initialized in the same order they are in the file, therefore, Aircraft should appear after Airplane
The code needs to pass the parameter to the base class's primary constructor. Since it does not, it receives a null
Abstract function always returns null
A superclass is initialized before its subclass. Therefore, name has not been set before it is rendered

reference discussion

Q3. Kotlin interfaces and abstract classes are very similar. What is one thing abstract class can do that interfaces cannot?

Only abstract classes are inheritable by subclasses
Only abstract classes can inherit from multiple superclasses
Only abstract classes can have abstract methods
Only abstract classes can store state

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Q4. Inside an extension function, what is the name of the variable that corresponds to the receiver object

The variable is named it
The variable is named this
The variable is named receiver
The variable is named default

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Q5. Your application has an add function. How could you use its invoke methods and display the results?

fun add(a: Int, b: Int): Int {
  return a + b
}

println(add(5,10).invoke())
println(::add.invoke(5, 10))
println(::add.invoke{5, 10})
println(add.invoke(5,10))

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Q6. What is the entry point for a Kotlin application?

fun static main(){}
fun main(){}
fun Main(){}
public static void main(){}

Q7. You are writing a console app in Kotlin that processes test entered by the user. If the user enters an empty string, the program exits. Which kind of loop would work best for this app? Keep in mind that the loop is entered at least once

a do..while loop
a for loop
a while loop
a forEach loop

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Q8. You pass an integer to a function expecting type Any. It works without issue. Why is a primitive integer able to work with a function that expects an object?

fun showHashCode(obj: Any){
  println("${obj.hashCode()}")
}
fun main() {
  showHashCode(1)
}

While the code runs, it does not produce correct results
The integer is always a class
The compiler runs an implicit .toClass() method on the integer
The integer is autoboxed to a Kotlin Int class

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Q9. You have started a long-running coroutine whose job you have assigned to a variable named task. If the need arose, how could you abort the coroutine?

val task = launch {
  // long running job
}

task.join()
task.abort()
job.stop()
task.cancel()

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Q10. You are attempting to assign an integer variable to a long variable, but Kotlin compiler flags it as an error. Why?

You must wrap all implicit conversion in a try/catch block
You can only assign Long to an Int, not the other way around
There is no implicit conversion from Int to Long
All integers in Kotlin are of type Long

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Q11. You have written a snippet of code to display the results of the roll of a six-sided die. When the die displays from 3 to 6 inclusive, you want to display a special message. Using a Kotlin range, what code should you add?

when (die) {
  1 -> println("die is 1")
  2 -> println("die is 2")
  ___ -> println("die is between 3 and 6")
  else -> println("die is unknown")
}

3,4,5,6
in 3..6
3 : 6
{3,4,5,6}

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Q12. The function typeChecker receives a parameter obj of type Any. Based upon the type of obj, it prints different messages for Int, String, Double, and Float types; if not any of the mentioned types, it prints "unknown type". What operator allows you to determine the type of an object?

instanceof
is
typeof
as

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Q13. This code does not print any output to the console. What is wrong?

firstName?.let {
  println("Greeting $firstname!")
}

A null pointer exception is thrown
firstName is equal to null
firstName is equal to an empty string
firstName is equal to Boolean false

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Q14. You have a function simple() that is called frequently in your code. You place the inline prefix on the function. What effect does it have on the code?

inline fun simple(x: Int): Int{
  return x * x
}

fun main() {
  for(count in 1..1000) {
    simple(count)
  }
}

The code will give a stack overflow error
The compiler warns of insignificant performance impact
The compiler warns of significant memory usage
The code is significantly faster

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Q15. How do you fill in the blank below to display all of the even numbers from 1 to 10 with least amount of code?

for (_____) {
  println("There are $count butterflies.")
}

count in 1..10
count in 2..10 step 2
count in 1..10 % 2
var count=2; count <= 10; count+=2

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Q16. What value is printed by println()?

val set = setOf("apple", "pear", "orange", "apple")
println(set.count())

3
4
1
5

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Q17. Which line of code shows how to display a nullable string's length and shows 0 instead of null?

println(b!!.length ?: 0)
println(b?.length ?: 0)
println(b?.length ?? 0)
println(b == null? 0: b.length)

Q18. In the file main.kt, you are filtering a list of integers and want to use an already existing function, removeBadValues. What is the proper way to invoke the function from filter in the line below?

val list2 = (80..100).toList().filter(_____)

::removeBadValues
GlobalScope.removeBadValues()
Mainkt.removeBadValues
removeBadValues

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Q19. Which code snippet correctly shows a for loop using a range to display "1 2 3 4 5 6"?

for(z in 1..7) println("$z ")
for(z in 1..6) print("$z ")
for(z in 1 to 6) print("$z ")
for(z in 1..7) print("$z ")

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Q20. You are upgrading a Java class to Kotlin. What should you use to replace the Java class's static fields?

an anonymous object
a static property
a companion object
a backing field

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Q21. Your code need to try casting an object. If the cast is not possible, you do not want an exception generated, instead you want null to be assigned. Which operator can safely cast a value?

as?
??
is
as

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Q22. Kotlin will not compile this code snippet. What is wrong?

class Employee
class Manager : Employee()

In order to inherit from a class, it must be marked open
In order to inherit from a class, it must be marked public
In order to inherit from a class, it must be marked sealed
In order to inherit from a class, it must be marked override

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Q23. Which function changes the value of the element at the current iterator location?

change()
modify()
set()
assign()

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Q24. From the Supervisor subclass, how do you call the Employee class's display() method?

open class Employee(){
  open fun display() = println("Employee display()")
}
class Supervisor : Employee() {
  override fun display() {
    println("Supervisor display()")
  }
}

Employee.display()
::display()
super.display()
override.display()

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Q25. The code below compiled and executed without issue before the addition of the line declaring errorStatus. Why does this line break the code?

sealed class Status(){
  object Error : Status()
  class Success : Status()
}
fun main(){
  var successStatus = Status.Success()
  var errorStatus = Status.Error()
}

StatusError is an object, not a class and cannot be instantiated
Only one instance of the class Status can be instantiated at a time
Status.Error must be declared as an immutable type
Status.Error is pribate to class and cannot be declared externally

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Q26. The code below is expected to display the numbers from 1 to 10, but it does not. Why?

val seq = sequence { yieldAll(1..20) }
  .filter { it < 11 }
  println(seq)

You cannot assign a sequence to a variable
To produce result, a sequence must have terminal operation. In this case, it needs a .toList()
The .filter{ it < 11 } should be .filter{ it > 11 }
The yieldAll(1..20) should be yieldAll(1..10)

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Q27. What three methods does this class have?

class Person

equals(), hashCode(), and toString()
equals(), toHash(), and super()
print(), println(), and toString()
clone(), equals(), and super()

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Q28. Which is the proper way to declare a singleton named DatabaseManager?

object DatabaseManager {}
singleton DatabaseManager {}
static class DatabaseManager {}
data class DatabaseManager {}

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Q29. In order to subclass the Person class, what is one thing you must do?

abstract class Person(val name: String) {
  abstract fun displayJob(description: String)
}

The subclass must be marked sealed
You must override the displayJob() method
You must mark the subclass as final
An abstract class cannot be extended, so you must change it to open

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Q30. The code snippet below translates a database user to a model user. Because their names are both User, you must use their fully qualified names, which is cumbersome. You do not have access to either of the imported classes' source code. How can you shorten the type names?

import com.tekadept.app.model.User
import com.tekadept.app.database.User

class UserService{
  fun translateUser(user: com.tekadept.app.database.User): User =
    com.tekadept.app.model.User("${user.first} ${user.last}")
}

Use import as to change the type name
Create subtypes with shorter names
Create interfaces with shorter names
Create extension classes with shorter names

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Q31. Your function is passed by a parameter obj of type Any. Which code snippet shows a way to retrieve the original type of obj, including package information?

obj.classInfo()
obj.typeInfo()
obj::class.simpleName
obj::class

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Q32. Which is the correct declaration of an integer array with a size of 5?

val arrs[5]: Int
val arrs = IntArray(5)
val arrs: Int[5]
val arrs = Array<Int>(5)

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Q33. You have created a class that should be visible only to the other code in its module. Which modifier do you use?

internal
private
public
protected

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Q34. Kotlin has two equality operators, == and ===. What is the difference?

== determines if two primitive types are identical. === determines if two objects are identical
== determines if two references point to the same object. === determines if two objects have the same value
== determines if two objects have the same value. === determines if two strings have the same value
== determines if two objects have the same value. === determines if two references point to the same object

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Q35. Which snippet correctly shows setting the variable max to whichever variable holds the greatest value, a or b, using idiomatic Kotlin?

val max3 = a.max(b) (Extension Function is One of the idiomatic Solutions in Kotlin)
val max = a > b ? a : b
val max = if (a > b) a else b
if (a > b) max = a else max = b

Q36. You have an enum class Signal that represents the state of a network connection. You want to print the position number of the SENDING enum. Which line of code does that?

enum class Signal { OPEN, CLOSED, SENDING }

println(Signal.SENDING.position())
println(Signal.SENDING.hashCode())
println(Signal.SENDING)
println(Signal.SENDING.ordinal)

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Q37. Both const and @JvmField create constants. What can const do that @JvmField cannot?

class Detail {
  companion object {
    const val COLOR = "Blue"
    @JvmField val SIZE = "Really Big"
  }
}

const is compatible with Java, but @JvmField is not
The compiler will inline const so it is faster and more memory efficient
Virtually any type can be used with const but not @JvmField
const can also be used with mutable types

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Q38. You have a when expression for all of the subclasses of the class Attribute. To satisfy the when, you must include an else clause. Unfortunately, whenever a new subclass is added, it returns unknown. You would prefer to remove the else clause so the compiler generates an error for unknown subtypes. What is one simple thing you can do to achieve this?

open class Attribute
class Href: Attribute()
class Src: Attribute()
class Alt: Attribute()

fun getAttribute(attribute: Attribute) : String {
  return when (attribute) {
    is Href -> "href"
    is Alt -> "alt"
    is Src -> "src"
    else -> "unknown"
  }
}

Replace open with closed
Replace open with sealed
Replace open with private
Replace open with public

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Q39. You would like to know each time a class property is updated. Which code snippet shows a built-in delegated property that can accomplish this?

Delegates.watcher()
Delegates.observable()
Delegates.rx()
Delegates.observer()

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Q40. Why doesn't this code compile?

val addend = 1
infix fun Int.add(added: Int=1) = this + addend
fun main(){
  val msg = "Hello"
  println( msg shouldMatch "Hello")
  println( 10 multiply 5 + 2)
  println( 10 add 5)
}

infix function must be marked public
In Kotlin, add is a keyword
Extension functions use it, not this, as the default parameter name
infix functions cannot have default values

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Q41. What is the correct way to initialize a nullable variable?

val name = null
var name: String
val name: String
val name: String? = null

Q42. Which line of code is a shorter, more idiomatic version of the displayed snippet?

val len: Int = if (x != null) x.length else -1

val len = x?.let{x.len} else {-1}
val len = x!!.length ?: -1
val len:Int = (x != null)? x.length : -1
val len = x?.length ?: -1

Q43. You are creating a Kotlin unit test library. What else should you add to make the following code compile without error?

fun String.shouldEqual(value: String) = this == value
fun main(){
  val msg = "test message"
  println(msg shouldEqual "test message")
}

The extension function should be marked public
Add the prefix operator to the shouldMatch extension function
The code is not legal in Kotlin (should be println(msg.shouldEqual("test message")))
Add the prefix infix to the shouldMatch extension function

Q44. What is the difference between the declarations of COLOR and SIZE?

class Record{
  companion object {
    const val COLOR = "Red"
    val SIZE = "Large"
  }
}

Since COLOR and SIZE are both immutable, they are identical internally
Both are immutable, but the use of the keyword const makes COLOR slower and less space efficient than SIZE
const makes COLOR faster, but not compatible with Java. Without const, SIZE is still compatible with Java
Both are immutable, but the use of the keyword const makes COLOR faster and more space efficient than SIZE

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Q45. Why does not this code snippet compile?

class Cat (name: String) {
  fun greet() { println("Hello ${this.name}") }
}

fun main() {
  val thunderCat = Cat("ThunderCat")
  thunderCat.greet()
}

Because name is a class parameter, not a property-it is unresolved main().
In order to create an instance of a class, you need the keyword new
The reference to name needs to be scoped to the class, so it should be this.name
Classes cannot be immutable. You need to change var to val

Note: By default, constructor parameters can only be used in the initializer blocks or property initializers declared in the class body. Therefore, to let the greet function have access to the name parameter, it should be declared as a property: class Cat (val name: String) { ... }

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Q46. The code below shows a typical way to show both index and value in many languages, including Kotlin. Which line of code shows a way to get both index and value more idiomatically?

var ndx = 0;
for (value in 1..5){
  println("$ndx - $value")
  ndx++
}

for( (ndx, value) in (1..20).withIndex() ){
for( (ndx, value) in (1..20).pair() ){
for( Pair(ndx, value) in 1..20 ){
for( (ndx, value) in *(1..20) ){

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Q47. The Kotlin .. operator can be written as which function?

a.from(b)
a.range(b)
a.rangeTo(b)
a.to(b)

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Q48. How can you retrieve the value of the property codeName without referring to it by name or destructuring?

data class Project(var codeName: String, var version: String)
fun main(){
  val proj = Project("Chilli Pepper", "2.1.0")
}

proj.0
proj[0]
proj[1]
proj.component1()

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Q49. This function generates Fibonacci sequence. Which function is missing?

fun fibonacci() = sequence {
  var params = Pair(0, 1)
  while (true) {
    ___(params.first)
    params = Pair(params.second, params.first + params.second)
  }
}

with()
yield()
skip()
return()

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Q50. In this code snippet, why does the compiler not allow the value of y to change?

for(y in 1..100) y+=2

y must be declared with var to be mutable
y is an implicitly immutable value
y can change only in a while loop
In order to change y, it must be declared outside of the loop

Q51. You have created a data class, Point, that holds two properties, x and y, representing a point on a grid. You want to use the hash symbol for subtraction on the Point class, but the code as shown will not compile. How can you fix it?

data class Point(val x: Int, val y: Int)

operator fun Point.plus(other: Point) = Point(x + other.x, y + other.y)
operator fun Point.hash(other: Point) = Point(x - other.x, y - other.y)

fun main() {
    val point1 = Point(10, 20)
    val point2 = Point(20, 30)
    println(point1 + point2)
    println(point1 # point2)
}

You cannot; the hash symbol is not a valid operator.
You should replace the word hash with octothorpe, the actual name for the symbol.
You should use minus instead of hash, then type alias the minus symbol.
You need to replace operator with the word infix.

Q52. This code snippet compiles without error, but never prints the results when executed. What could be wrong?

val result = generateSequence(1) { it + 1 }.toList()
println(result)

The sequence lacks a terminal operation.
The sequence is infinite and lacks an intermediate operation to make it finite.
The expression should begin with generateSequence(0).
The it parameter should be replaced with this.

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Q53. An error is generated when you try to compile the following code. How should you change the call to printStudents to fix the error?

fun main() {
    val students = arrayOf("Abel", "Bill", "Cindy", "Darla")
    printStudents(students)
}

fun printStudents(vararg students: String) {
    for(student in students) println(student)
}

printStudents(students.toList())
printStudents(students!!)
printStudents(*students)
printStudents(students[])

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Q54. Both y and z are immutable references pointing to fixed-size collections of the same four integers. Are there any differences?

val y = arrayOf(10, 20, 30, 40)
val z = listOf(10, 20, 30, 40)

You can modify the contents of the elements in y but not z.
There are not any differences. y and z are a type alias of the same type.
You add more elements to z since it is a list.
You can modify the contents of the elements in z but not y.

Q55. The code snippet compile and runs without issue, but does not wait for the coroutine to show the "there" message. Which line of code will cause the code to wait for the coroutine to finish before exiting?

fun main() = runBlocking {
    val task = GlobalScope.launch {
        delay(1000L)
        println("there")
    }
    println("Hello,")
}

task.complete()
task.wait()
task.join()
task.cancel()

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Q56. You would like to group a list of students by last name and get the total number of groups. Which line of code accomplishes this, assuming you have a list of the Student data class?

data class Student(val firstName: String, val lastName: String)

println(students.groupBy{ it.lastName }.count())
println(students.groupBy{ it.lastName.first() }.fold().count())
println(students.groupingBy{ it.lastName.first() }.count())
println(students.groupingBy{ it.lastName.first() }.size())

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Q57. Class BB inherits from class AA. BB uses a different method to calculate the price. As shown, the code does not compile. What changes are needed to resolve the compilation error?

open class AA() {
     var price: Int = 0
        get() = field + 10
}
class BB() : AA() {
     var price: Int = 0
        get() = field + 20
}

You need to add a lateinit modifier to AA.price.
You simply need to add an override modifier to BB.price.
You need to add an open modifier to AA.price and an override modifier to BB.price.
You need to add a public modifier to AA.price and a protected modifier to BB.price.

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Q58. What is the output of this code?

val quote = "The eagle has landed."
println("The length of the quote is $quote.length")

The length of the quote is The eagle has landed.
A compilation error is displayed.
The length of the quote is 21
The length of the quote is The eagle has landed..length

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Q59. You have an unordered list of high scores. Which is the simple method to sort the highScores in descending order?

fun main() {
    val highScores = listOf(4000, 2000, 10200, 12000, 9030)

.sortedByDescending()
.descending()
.sortedDescending()
.sort("DESC")

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Q60. Your class has a property name that gets assigned later. You do not want it to be a nullable type. Using a delegate, how should you declare it?

lateinit var name: String // lateinit is modifier not delegate
var name: String by lazy
var name: String by Delegates.notNull()
var name: String? = null

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Q61. You want to know each time a class property is updated. If the new value is not within range, you want to stop the update. Which code snippet shows a built-in delegated property that can accomplish this?

Delegates.vetoable()
Delegates.cancellable()
Delegates.observer()
Delegates.watcher()

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Q62. Which line of code shows how to call a Fibonacci function, bypass the first three elements, grab the next six, and sort the elements in descending order?

val sorted = fibonacci().skip(3).take(6).sortedDescending().toList()
val sorted = fibonacci().skip(3).take(6).sortedByDescending().toList()
val sorted = fibonacci().skip(3).limit(6).sortedByDescending().toList()
val sorted = fibonacci().drop(3).take(6).sortedDescending().toList()

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Q63. You have two arrays, a and b. Which line combines a and b as a list containing the contents of both?

val a = arrayOf(1, 2, 3)
val b = arrayOf(100, 200, 3000)

val c = list of (a, b)
val c = a + b
val c = listOf(a+b)
val c = listOf(*a, *b)
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Q64. This code is occasionally throwing a null pointer exception (NPE). How can you change the code so it never throws as NPE?

println("length of First Name = ${firstName!!.length}")

Replace !!. with ?.
Replace !!. with ?:.
Surround the line with a try/catch block.
Replace !!. with ?.let.

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Q65. What is the execution order of init blocks and properties during initialization?

All of the properties are executed in order of appearance, and then the init blocks are executed.
The init blocks and properties are executed in the same order they appear in the code.
All of the init blocks are executed in order of appearance, and then the properties are executed.
The order of execution is not guaranteed, so code should be written accordingly.

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Q66. Both const and @JvmField create constants. What can @JvmField do that const cannot?

class Styles {
  companion object {
    const val COLOR = "Blue"
      @JvmField val SIZE = "Really big"
   }
}

const works only with strings and primitives. @JvmField does not have that restriction.
@JvmField works as a top-level variable, but const works only in a class.
@JvmField is compatible with Java, but const is not.
@JvmField is always inlined for faster code.

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Q67. What are the two ways to make a coroutine's computation code cancellable?

Call the yield() function or check the isActive property.
Call the cancelled() function or check the isActive property.
Call the stillActive() function or check the isCancelled property.
Call the checkCancelled() function or check the isCancelled property.

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Q68. Given the code below, how can you write the line this.moveTo("LA") more concisely?

data class Student (val name: String, var location: String) {
  fun moveTo (newLoc: String) { location = newLoc }

}

fun main() {

  Student ("Snow", "Cologne").run {

  this.moveTo ("LA")

}

moveTo("LA")
::moveTo("LA")
_.moveTo("LA")
it.moveTo("LA")

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Q69. For the Product class you are designing, you would like the price to be readable by anyone, but changeable only from within the class. Which property declaration implements your design?

Option 1

var price: Int = 0
  public get()
  private set

Option 2

var price: Int = 0
  private set

Option 3

var price: Int = 0
  val set

Option 4

val price: Int=0

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Q70. What will happen when you try to build and run this code snippet?

class SpecialFunction : () -> Unit {
  override fun invoke() {
    println("Invoked from an instance.")
  }
}
fun main() {
  try { SpecialFunction()() }
  catch (ex: Exception) { println("An error occurred") }
}

A syntax error occurs due to the line SpecialFunction()().
The message "An Error occurred" is displayed.
The message "Invoked from an instance." is displayed. // the second "()" is equals to .invoke()
A compile error occurs. You cannot override the invoke() method.

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Q71. Which statement declares a variable mileage whose value never changes and is inferred to be an integer?

val mileage:Int = 566
var mileage:Int = 566
val mileage = 566 (Note: inferred)
const int mileage = 566

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Q72. What is the preferred way to create an immutable variable of type long?

var longInt = 10L
const long longInt = 10
val longInt = 10L
val longInt:Long = 10

Q73. Which line converts the binaryStr, whish contain only 0s and 1s, to an integer representing its decimal value?

val binaryStr = "00001111"

val myInt = toInt(binaryStr)
val myInt = binaryStr.toInt("0b")
val myInt = binaryStr.toInt()
val myInt = binaryStr.toInt(2)

Q74. In a Kotlin program, which lines can be marked with a label

Any program line can be marked with a label
Any statement can be marked with a label
Any expression can be marked with a label
Only the beginning of loops can be marked with a label

article -
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Q75. All classes in Kotlin inherit from which superclass?

Default
Super
Any
Object

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Q76. You have written a function, sort(), that should accept only collections that implement the `Comparable` interface. How can you restrict the function?

fun sort(list: List<T>): List <T> {
    return list.sorted()
}

Add <T -> Comparable<T>> between the fun keyword and the function name
Add Comparable<T> between the fun keyword and the function name
Add <T : Comparable<T>> between the fun keyword and the function name
Add <T where Comparable<T>> between the fun keyword and the function name

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Q77. Kotlin classes are final by default. What does final mean?

final means that you cannot use interfaces with this class.
final means that this is the only file that can use the class.
final means that you cannot extend the class.
final classes cannot be used in the finally section of a try/catch block.

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Q78. You have created an array to hold three strings. When you run the code bellow, the compiler displays an error. Why does the code fail?

val names = arrayOf<String>(3)
names[3]= "Delta"

Arrays use zero-based indexes. The value 3 is outside of the array's bounds
You accessed the element with an index but should have used.set().
You declared the array with val but should have used var
You cannot changes the value of an element of an array. You should have used a mutable list.

Q79. If a class has one or more secondary constructors, what must each of them do?

Each secondary constructor must call super().
Each secondary constructor must call base().
Each secondary constructor must directly or indirectly delegate to the primary.
Each secondary constructor must have the same name as the class.

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Q80. When you can omit constructor keyword from the primary constructor?

It can be omitted only if an init block is defined.
It can be omitted anytime; it is not mandatory.
It can be omitted if secondary constructors are defined.
It can be omitted when the primary constructor does not have any modifiers or annotations.

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Q81. How many different kinds of constructors are available for kotlin classes?

two.
none.
four.
one.

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Q82. What is the default visibility modifier in Kotlin?

protected
private
internal
public

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Q83. The code below compiles and executes without issue, but is not idiomatic kotlin. What is a better way to impelement the `printlln()`?

fun main() {
  val name: String = "Amos"
  val grade: Float = 95.5f
  println("My name is " + name + ". I score " + grade + " points on the last coding quiz.")
}

Use new printf().
Use string.format instead.
Use string append instead.
Use string templates instead.

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Q84. You have enum class Signal that represent state of network connection. You want to iterate over each the member of the enum. Which line of code shows how to do that `?

Signal.sequence().
Signal.toArray().
Signal.values().
Signal.toList().

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Q85. You'd like to create multiline string that includes the carriage return characther. What should you use to enclose the string?

Double quotes("").
Single quotes(').
Tripple quote(""").
Backticks().

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Q86. You want your class member to be visible to subclasses. Which modifier do you use?

Public.
Protected.
Internal.
Private.

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Q87. which line of code shows how to create a finite sequence of the numbers 1 to 99 and then convert it into a list?

val lessThan99 = generateSequence(1){ if (it < 99) it + 1 else null }.toList().
val lessThan99 = generateSequence(0){ if (it < 99)}.toList().
val lessThan99 = generateSequence(1..9){ if (it < 99) it + 1 else null }.toList().
val lessThan99 = listOf{1..99}.asSequence().toList()

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Q88. What is wrong with this class definition?

class Empty

The class is properly defined, so nothing is wrong with it.
The parentheses are missing-it should be declared as class Empty().
Empty is a Kotlin keyword, so the code will generate an error when compiled.
The curely braces are missing from the declaration of Empty.

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Q89. What is a higher-order function in Kotlin?

A higher-order function is a function that returns a value other than Unit.
A higher-order function is the function that appears before others in a file.
A higher-order function is one that can be stored in a variable.
A higher-order function is a function that takes a function as a parameter, or returns a function.

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Kotlin

Q1. You would like to print each score on its own line with its cardinal position. Without using var or val, which method allows iteration with both the value and its position?

Q2. When the Airplane class is instantiated, it displays Aircraft = null, not Aircraft = C130 why?

Q3. Kotlin interfaces and abstract classes are very similar. What is one thing abstract class can do that interfaces cannot?

Q4. Inside an extension function, what is the name of the variable that corresponds to the receiver object

Q5. Your application has an add function. How could you use its invoke methods and display the results?

Q6. What is the entry point for a Kotlin application?

Q7. You are writing a console app in Kotlin that processes test entered by the user. If the user enters an empty string, the program exits. Which kind of loop would work best for this app? Keep in mind that the loop is entered at least once

Q8. You pass an integer to a function expecting type Any. It works without issue. Why is a primitive integer able to work with a function that expects an object?

Q9. You have started a long-running coroutine whose job you have assigned to a variable named task. If the need arose, how could you abort the coroutine?

Q10. You are attempting to assign an integer variable to a long variable, but Kotlin compiler flags it as an error. Why?

Q11. You have written a snippet of code to display the results of the roll of a six-sided die. When the die displays from 3 to 6 inclusive, you want to display a special message. Using a Kotlin range, what code should you add?

Q12. The function typeChecker receives a parameter obj of type Any. Based upon the type of obj, it prints different messages for Int, String, Double, and Float types; if not any of the mentioned types, it prints "unknown type". What operator allows you to determine the type of an object?

Q13. This code does not print any output to the console. What is wrong?

Q14. You have a function simple() that is called frequently in your code. You place the inline prefix on the function. What effect does it have on the code?

Q15. How do you fill in the blank below to display all of the even numbers from 1 to 10 with least amount of code?

Q16. What value is printed by println()?

Q17. Which line of code shows how to display a nullable string's length and shows 0 instead of null?

Q18. In the file main.kt, you are filtering a list of integers and want to use an already existing function, removeBadValues. What is the proper way to invoke the function from filter in the line below?

Q19. Which code snippet correctly shows a for loop using a range to display "1 2 3 4 5 6"?

Q20. You are upgrading a Java class to Kotlin. What should you use to replace the Java class's static fields?

Q21. Your code need to try casting an object. If the cast is not possible, you do not want an exception generated, instead you want null to be assigned. Which operator can safely cast a value?

Q22. Kotlin will not compile this code snippet. What is wrong?

Q23. Which function changes the value of the element at the current iterator location?

Q24. From the Supervisor subclass, how do you call the Employee class's display() method?

Q25. The code below compiled and executed without issue before the addition of the line declaring errorStatus. Why does this line break the code?

Q26. The code below is expected to display the numbers from 1 to 10, but it does not. Why?

Q27. What three methods does this class have?

Q28. Which is the proper way to declare a singleton named DatabaseManager?

Q29. In order to subclass the Person class, what is one thing you must do?

Q30. The code snippet below translates a database user to a model user. Because their names are both User, you must use their fully qualified names, which is cumbersome. You do not have access to either of the imported classes' source code. How can you shorten the type names?

Q31. Your function is passed by a parameter obj of type Any. Which code snippet shows a way to retrieve the original type of obj, including package information?

Q32. Which is the correct declaration of an integer array with a size of 5?

Q33. You have created a class that should be visible only to the other code in its module. Which modifier do you use?

Q34. Kotlin has two equality operators, == and ===. What is the difference?

Q35. Which snippet correctly shows setting the variable max to whichever variable holds the greatest value, a or b, using idiomatic Kotlin?

Q36. You have an enum class Signal that represents the state of a network connection. You want to print the position number of the SENDING enum. Which line of code does that?

Q37. Both const and @JvmField create constants. What can const do that @JvmField cannot?

Q39. You would like to know each time a class property is updated. Which code snippet shows a built-in delegated property that can accomplish this?

Q40. Why doesn't this code compile?

Q41. What is the correct way to initialize a nullable variable?

Q42. Which line of code is a shorter, more idiomatic version of the displayed snippet?

Q43. You are creating a Kotlin unit test library. What else should you add to make the following code compile without error?

Q44. What is the difference between the declarations of COLOR and SIZE?

Q45. Why does not this code snippet compile?

Q46. The code below shows a typical way to show both index and value in many languages, including Kotlin. Which line of code shows a way to get both index and value more idiomatically?

Q47. The Kotlin .. operator can be written as which function?

Q48. How can you retrieve the value of the property codeName without referring to it by name or destructuring?

Q49. This function generates Fibonacci sequence. Which function is missing?

Q50. In this code snippet, why does the compiler not allow the value of y to change?

Q51. You have created a data class, Point, that holds two properties, x and y, representing a point on a grid. You want to use the hash symbol for subtraction on the Point class, but the code as shown will not compile. How can you fix it?

Q52. This code snippet compiles without error, but never prints the results when executed. What could be wrong?

Q53. An error is generated when you try to compile the following code. How should you change the call to printStudents to fix the error?

Q54. Both y and z are immutable references pointing to fixed-size collections of the same four integers. Are there any differences?

Q55. The code snippet compile and runs without issue, but does not wait for the coroutine to show the "there" message. Which line of code will cause the code to wait for the coroutine to finish before exiting?

Q56. You would like to group a list of students by last name and get the total number of groups. Which line of code accomplishes this, assuming you have a list of the Student data class?

Q57. Class BB inherits from class AA. BB uses a different method to calculate the price. As shown, the code does not compile. What changes are needed to resolve the compilation error?

Q58. What is the output of this code?

Q59. You have an unordered list of high scores. Which is the simple method to sort the highScores in descending order?

Q60. Your class has a property name that gets assigned later. You do not want it to be a nullable type. Using a delegate, how should you declare it?

Q61. You want to know each time a class property is updated. If the new value is not within range, you want to stop the update. Which code snippet shows a built-in delegated property that can accomplish this?

Q62. Which line of code shows how to call a Fibonacci function, bypass the first three elements, grab the next six, and sort the elements in descending order?

Q63. You have two arrays, a and b. Which line combines a and b as a list containing the contents of both?

Q64. This code is occasionally throwing a null pointer exception (NPE). How can you change the code so it never throws as NPE?

Q65. What is the execution order of init blocks and properties during initialization?

Q66. Both const and @JvmField create constants. What can @JvmField do that const cannot?

Q67. What are the two ways to make a coroutine's computation code cancellable?

Q68. Given the code below, how can you write the line this.moveTo("LA") more concisely?

Q69. For the Product class you are designing, you would like the price to be readable by anyone, but changeable only from within the class. Which property declaration implements your design?

Q70. What will happen when you try to build and run this code snippet?

Q71. Which statement declares a variable mileage whose value never changes and is inferred to be an integer?

Q72. What is the preferred way to create an immutable variable of type long?

Q73. Which line converts the binaryStr, whish contain only 0s and 1s, to an integer representing its decimal value?

Q74. In a Kotlin program, which lines can be marked with a label

Q76. You have written a function, sort(), that should accept only collections that implement the `Comparable` interface. How can you restrict the function?

Q83. The code below compiles and executes without issue, but is not idiomatic kotlin. What is a better way to impelement the `printlln()`?