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
+
使用ranges
使用 in 操作符检查数值是否在某个范围内:
+
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:
+
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:
+
fun main(args: Array<String>) {
for (x in 1..5) {
print(x)
}
}
或者使用步进:
+
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
+
使用集合
对一个集合进行迭代:
+
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
+
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:
+
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) }
}