Key Concepts

Question 1

Ranges

Answer 1

An interval that has a:

• start value
• end value

Common options for defining an interval:

• step(n)
• reversed()

val aToZ = “a”..”z”
val containsC = “c” in aToZ
1..9
val countDown = 100.downTo(0)
val rangeTo = 1.rangeTo(30)
val oddNumbers = rangeTo.step(2)
val countDownEvenNumbers s = (2..100).step(2).reversed()

Question 2

String Templates

Answer 2

Embed values, variables, or expressions inside a string
without pattern replacement or string concatendation
—————————————————————————————–

“Hello $firstName”

“Your name has ${name.length} characters”

Question 3

Loops

Answer 3

while(true)

for (k in list)

Question 4

Equality

Answer 4

referential

• structural
• ————————————–*

val sameReference = a === b

val structuralEquality = a == b
# == is null safe
# calls .equals() on each object

Question 5

Current Receiver

Answer 5

The object reference referred to
by the this keyword
—————————————————

• object to the left of the ​dot notation
• object of the class in which this function is defined
• OuterInstanceClass.this from nested classes

Question 6

visibility modifiers

Answer 6

private​
C only be accessed from the same file

protected
Visible only to other members of the class
or interface, including subclasses.
Cannot include top-level functions, classes or interfaces.
internal
Visible only from other classes, interfaces and functions
within the same IntelliJ, Maven or Gradle module.

Question 7

control flow as expressions

Answer 7

The following control flow blocks are expressions,
versus statements:

• if…else
• try…catch

fun isTuesday() {
 // must include the else clause
 if (LocalDate.now().getDayOfWeek() == "TUESDAY") true else false
}

val success = try {
readFile()
true
} catch (e: IOException) {
false
}

Question 8

null syntax

Answer 8

val firstName: String? // allow null value
val firstsName: String = null // compile time error

val firstName: String? = anyThing is String // blows up if anyThing is null
val firstName: String? = anyThing is? String // safe

Question 9

type checking
and casting

Answer 9

is
is?
smart casts
explicit casts
————————-

anyThing is String // will throw a runtime exception if anyThing is null

if (anyThing is String) {
println(anyThing.length)
}

Question 10

when

Answer 10

• asdfasdf
• —————————————————-*
• only exhaustive when used as an expression
• what is the danger of the else clause ?