Kotlin Quiz # 2

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())

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(

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

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()

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()

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)

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.

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.

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.

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

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

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(

Val myInt = binaryStr.toInt()

Val myInt = binaryStr.toInt(2)

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

All classes in Kotlin inherit from which superclass?

Default

Super

Any

Object

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): List { return list.sorted()}

Add Comparable> between the fun keyword and the function name

Add Comparable between the fun keyword and the function name

Add > between the fun keyword and the function name

Add > between the fun keyword and the function name

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.

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(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.

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.

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.

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

Two.

None.

Four.

One.

What is the default visibility modifier in Kotlin?

Protected

Private

Internal

Public