제어와 반복

1. for

val items = listOf("apple","banana","kiwifruit")

for (a in items) {

  println(a)

}

for (index in items.indices) {

  println("item at $index is ${items[index]}")

}

2. while

val items = listOf("apple", "banana", "kiwi")

var index=0

while (index < items.size) {

  println("item at $index is ${items[index]}")

  index++

}

3. when, 변수 형식에 구애받지 않는 switch

- case도 필요 없음, break없음

fun describe(obj: Any): String = 

when(obj) {

  1 -> "One"

  "Hello" -> "Greeting"

  is Long -> "Long"

  !is String -> "Not a String"

  else -> "Unknown"

}

return에도 사용가능

fun transform(color: String):Int {

  return when(color) {

    "Red"->0

    "Green"->1

    "Blue"->2

    else -> throw IllegalArgumentException("Invalid color param value")

  }

}

4. ranges

val x = 10

val y = 9

if (x in 1..y+1) {

  println("fits in range")

}

val list = listOf("a","b","c")

if (-1 !in 0..list.lastIndex) {

  println("-1 is out of range")

}

if (list.size !in list.indices) {

  println("list size is out of valid list indices range too")

}

for (x in 1..5) {print(x)}

for (x in 1..10 step 2) {print(x)}

for (x in 9 downTo 0 step 3) {print(x)}

for (x in 1 until 100) {print(x)}

5. collections

for (item in items) {println(item)}

when {"orange" in items -> println("juicy")

  "apple" in items -> println("apple is fine too")

}

fruits

.filter(it.startsWith("a")}

.sortedBy{it}

.map{it.toUpperCase()}

.forEach{println(it)}

6. try/catch

fun test() {

  val result = try{

    count()

  } catch(e:ArithmeticException){

    throw IllegalStateException(e)

  }

}