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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)
Q2. When the Airplane class is instantiated, it displays Aircraft = null, not Aircraft = C130 why?
abstract class Aircraft {
init { println("Aircraft = ${getName()}") }
abstract fun getName(): String
}
class Airplane(private val name: String) : Aircraft() {
override fun getName(): String = name
}
Classes are initialized in the same order they are in the file, therefore, Aircraft should appear after Airplane
The code needs to pass the parameter to the base class's primary constructor. Since it does not, it receives a null
Abstract function always returns null
A superclass is initialized before its subclass. Therefore, name has not been set before it is rendered
Q3. Kotlin interfaces ad abstract classes are very similar. What is one thing abstract class can do that interfaces cannot?
Only abstract classes are inheritable by subclasses
Only abstract classes can inherit from multiple superclasses
Q6. What is the entry point for a Kotlin application?
fun static main(){}
fun main(){}
fun Main(){}
public static void main(){}
Q7. You are writing a console app in Kotlin that processes test entered by the user. If the user enters an empty string, the program exits. Which kind of loop would work best for this app? Keep in mind that the loop is entered at least once
a do..while loop
a for loop
a while loop
a forEach loop
Q8. You pass an integer to a function expecting type Any. It works without issue. Why is a primitive integer able to work with a function that expects an object?
fun showHashCode(obj: Any){
println("${obj.hasCode()}")
}
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
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()
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
reference
All integers in Kotlin are of type Long
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")
___ -> printlin("die is between 3 and 6")
else -> printlin("dies is unknown")
}
Q12. The function typeChecker receiver 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
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?
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
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 $count butterflies.")
}
count in 1..10
count in 2..10 step 2
count in 1..10 % 2
var count=2; count <= 10; count+=2
Q16. What value is printed by println()?
val set = setOf("apple", "pear", "orange", "apple")
println(set.count())
Q17. Which line of code shows how to display a nullable string's length and shows 0 instead of null?
println(b!!.length ?: 0)
println(b?.length ?: 0)
println(b?.length ?? 0)
println(b == null? 0: b.length)
Q18. In the file main.kt, you ae filtering a list of integers and want to use an already existing function, removeBadValues. What is the proper way to invoke the function from filter in the line below?
Q19. Which code snippet correctly shows a for loop using a range to display "1 2 3 4 5 6"?
for(z in 1..7) println("$z ")
for(z in 1..6) print("$z ")
for(z in 1 to 6) print("$z ")
for(z in 1..7) print("$z ")
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
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
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
Q23. Which function changes the value of the element at the current iterator location?
change()
modify()
set()
assign()
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()
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
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 }
Q28. Which is the proper way to declare a singleton named DatabaseManager?
object DatabaseManager {}
singleton DatabaseManager {}
static class DatabaseManager {}
data class DatabaseManager {}
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
reference
You must mark the subclass as final
An abstract class cannot be extended, so you must change it to open
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
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?
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
reference
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)
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?
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
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?