Kotlin流程控制、循环

一、流程控制

1.if

val i = 1
if (i > 0) {
    print("Big")
} else {
    print("Small")
}

 使用if,赋值。

val i = 1
val message = if (i > 0) "Big" else "Small"

print(message)

 

fun getLength(text: String?): Int {
  return if (text != null) text.length else 0
}

 上边的简写，Elvis 表达式；

fun getLength(text: String?): Int {
  return text?.length ?: 0
}

 2.when

val i: Int = 1

when(i) {
    1 -> print("一")
    2 -> print("二")
    else -> print("i 不是一也不是二")
}

 

val i: Int = 1

val message = when(i) {
    1 -> "一"
    2 -> "二"
    else -> "i 不是一也不是二" // 如果去掉这行，会报错
}

print(message)

二、循环

1、for

 val oneToThree = 1..3
    for (i in oneToThree) {
        println(i)
    }

    for (i in 6 downTo 0 step 3) {
        println(i)
    }

    for (i in 0..10) {
        println(i) //012345678910
    }
    for (i in 0 until 10) {
        println(i) //0123456789
    }
    for (i in 0..10 step 2) {
        print(i) //0 2 4 6 8 10
    }
    //获取元素
    var abc = listOf("a", "b", "c")
    for (i in abc) {
        print(i)
    }
    //    获取下标
    for (index in abc.indices) {
        print("$index") // 0 1 2
    }
    //    获取元素和下标
    for ((index, value) in abc.withIndex()) {
        print("$index:$value ")  //0:a 1:b 2:c
    }

 2、while

var i = 0
while (i <= 2) {
    println(i)
    i++
}

var j = 0
do {
    println(j)
    j++
} while (j <= 2)