Loops in Kotlin.
enum class Season {
SPRING, SUMMER, AUTUMN, WINTER
}
fun main() {
// for (int i = 0; i < 10; i++) does not exist in Kotlin. Use ranges instead:
for (i in 1..20) {
}
val range = 1..5
val charRange = 'a'..'z' // Valid as long as values are comparable
val stringRange = "ABC".."XYZ" // Valid as long as values are comparable
println(3 in range) // true
println('q' in charRange) // true
println("CCC" in stringRange) // true
println("CCCCCC" in stringRange) // Still lower than XYZ
println("ZZZZZZ" in stringRange)// false
println(32 !in 1..10) // Not in the range
println("=======")
val backwardRange = 5.downTo(1)
println(5 in backwardRange) // true
val stepRange = 3..15 // Define initial range
val step3 = stepRange.step(3) // Take the first and then every third value
for (i in step3) println(i)
println("=======")
// Or
for (i in 0..20 step 4) println(i)
println("=======")
val reverseStep = step3.reversed() // Only works for integers
for (i in reverseStep) println(i)
println("=======")
// Or
for (i in 20 downTo 15) println(i) // Decrement
println("=======")
for (i in 20 downTo 10 step 5) println(i) // Decrement in steps
println("=======")
for (i in 1 until 10) println(i) // Excludes last number in range
println("=======")
// To loop through a String range we need an iterator, which is included in the String class:
val aString = "howdy"
for (a in aString) println(a)
println("=======")
val seasons = arrayOf("Spring", "Summer", "Autumn", "Winter")
for (season in seasons) println(season)
println("=======")
println("whatever" !in seasons)
println("=======")
val bString = "hello"
println('e' in bString)
println('e' !in bString)
println("=======")
// Long way
for (index in seasons.indices) {
println("${seasons[index]} is season number ${index + 1}")
}
println("=======")
// Or
seasons.forEach { println(it) } // <- Lambda expression
seasons.forEachIndexed { index, value -> println("$value is season number $index")} // Equivalent to above expression
println("=======")
// We can name loops
// Say we want to break out of both the j & k loops when k hits 7...
for (i in 1..3) {
println("i = $i")
jloop@ for (j in 1..4) { // Label the loop
println("j = $j")
for (k in 5..10) {
println("k = $k")
if (k == 7) {
break@jloop // Call the @jloop. Also works with continue@jloop
}
}
}
}
println("=======")
// Can get out of hand easily so only use when necessary
// if (expression) in Kotlin can evaluate to a value, unlike Java
// Makes ternary operator ( String name = case.equals("uppercase") ? "JOHN" : "john"; ) obsolete
val someCondition = 69 < 22
var num: Int
if (someCondition) { // No return
num = 50
} else {
num = 592
}
// Or
var num2 = if (someCondition) 50 else 592 // returns the int value. Must provide else if using an expression
// When statement is enhanced switch statement
val num3 = 200
val y = 400
when(num3) {
100, 600 -> println("100") // If value is 100 or 600
200 -> println("200")
in 201..300 -> println("In range 201 to 300") // Ranges allowed
y + 80 -> println("80 more than y") // Expressions allowed
else -> "Didn't match anything"
}
val obj1: Any = "I'm a string"
val obj2: Any = BigDecimal(25.2)
val obj3: Any = 45
val something: Any = obj2
if (something is String) println(something.toUpperCase()) // All of this
else if (something is BigDecimal) println(something.remainder(BigDecimal(10.5))) // can be replaced
else if (something is Int) println("${something - 22}") // by the following:
when (something) {
is String -> println(something.toUpperCase())
is BigDecimal -> println(something.remainder(BigDecimal(10.5)))
is Int -> println("${something - 22}")
}
// Can also evaluate to a value
var z = when (something) {
is String -> something.toUpperCase()
is BigDecimal -> something.remainder(BigDecimal(10.5))
is Int -> "${something - 22}"
else -> "No idea what type it is"
}
// Use with enums
val timeOfYear = Season.WINTER // See Season enum at top-level
val str = when(timeOfYear) { // No else required when enum constrains the options
Season.SPRING -> "Flowers are blooming"
Season.SUMMER -> "Sun is shining"
Season.AUTUMN -> "Leaves are falling"
Season.WINTER -> "It's snowing"
}
println(str)
// Can be used without a value - alternative to if..else:
val num4 = -50
val num5 = 25
if (num4 < num5) {
println("num4 is less than num5")
} else if (num4 > num5) {
println("num4 is greater than num5")
} else {
println("num4 = num5")
}
// Can be written as
when {
num4 < num5 -> println("num4 is less than num5")
num4 > num5 -> println("num4 is greater than num5")
else -> println("num4 = num5")
}
}
