kotlin 学习记录 基本语法 （2）

https://huanglizhuo.gitbooks.io/kotlin-in-chinese/content/GettingStarted/Basic-Syntax.html

使用循环

fun main(args: Array<String>) {  val items = listOf("apple", "banana", "kiwi")  for (item in items) {    println(item)  }}

或者

fun main(args: Array<String>) {  val items = listOf("apple", "banana", "kiwi")  for (index in items.indices) {    println("item at $index is ${items[index]}")  }}
使用 while 循环
fun main(args: Array<String>) {  val items = listOf("apple", "banana", "kiwi")  var index = 0  while (index < items.size) {    println("item at $index is ${items[index]}")    index++  }}
参看while循环
使用 when 表达式
fun describe(obj: Any): String =when (obj) {  1          -> "One"  "Hello"    -> "Greeting"  is Long    -> "Long"  !is String -> "Not a string"  else       -> "Unknown"}fun main(args: Array<String>) {  println(describe(1))  println(describe("Hello"))  println(describe(1000L))  println(describe(2))  println(describe("other"))}
参看when表达式
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使用ranges
使用 in 操作符检查数值是否在某个范围内：
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fun main(args: Array<String>) {  val x = 10  val y = 9  if (x in 1..y+1) {      println("fits in range")  }}
检查数值是否在范围外：
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fun main(args: Array<String>) {  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")  }}
在范围内迭代：
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fun main(args: Array<String>) {  for (x in 1..5) {    print(x)  }}
或者使用步进：
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fun main(args: Array<String>) {  for (x in 1..10 step 2) {    print(x)  }  for (x in 9 downTo 0 step 3) {    print(x)  }}
参看Ranges
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使用集合
对一个集合进行迭代：
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fun main(args: Array<String>) {  val items = listOf("apple", "banana", "kiwi")  for (item in items) {    println(item)  }}
使用 in 操作符检查集合中是否包含某个对象
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fun main(args: Array<String>) {  val items = setOf("apple", "banana", "kiwi")  when {    "orange" in items -> println("juicy")    "apple" in items -> println("apple is fine too")  }}
使用lambda表达式过滤和映射集合：
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fun main(args: Array<String>) {  val fruits = listOf("banana", "avocado", "apple", "kiwi")  fruits    .filter { it.startsWith("a") }    .sortedBy { it }    .map { it.toUpperCase() }    .forEach { println(it) }}