【Kotlin】Kotlin笔记2-程序的逻辑控制(if,when,循环语句)

Kotlin笔记-程序的逻辑控制

2. 程序的逻辑控制

• if条件语句

if

​​Example:​​

fun largerNumber3(num1: Int, num2: Int): Int {
    var value = 0
    if (num1 > num2) {
        value = num1
    } else
        value = num2

    return value
}

语法糖

fun largerNumber4(num1: Int, num2: Int): Int {
    val value = if (num1 > num2) {
        num1
    } else {
        num2
    }
    return value
}

fun largerNumber5(num1: Int, num2: Int): Int {
    return if (num1 > num2)
        num1
    else
        num2
}

fun largerNumber6(num1: Int, num2: Int) = if (num1 > num2) {
    num1
} else {
    num2
}

fun largerNumber7(num1: Int, num2: Int) = if (num1 > num2) num1 else num2

• when条件语句

when

​​Example if:​​

fun getScore(name: String) = if (name == "Tom") 86
else if (name == "Jim") 77
else if (name == "Jack") 95
else if (name == "Lily") 100
else 0

​​Example when:​​

fun getScore1(name: String) = when (name) {
    "Tom" -> 86
    "Jim" -> 77
    "Jack" -> 95
    "Lily" -> 100
    else -> 0
}

when允许传入任意类型参数,格式:

匹配值 -> { 执行逻辑 }

类型匹配

fun checkNumber(num: Number) {
    when (num) {
        is Int -> println("number is Int")
        is Double -> println("number is Double")
        else -> println("number not support")
    }
}

is = instanseof(Java)

不传参when

fun getScore2(name: String)=when{
    name=="Tom"->86
    name=="Jim"->77
    name=="Jack"->95
    name=="Lily"->100
    else->0
}

​​特殊场景 example:​​

name.startsWith("Tom")->86
    name=="Jim"->77
    name=="Jack"->95
    name=="Lily"->100
    else->0
}

• 循环语句

while

for ->for-in

闭区间

va range = 0..10 //[0,10]

fun circulation(){
    for (i in 1..10){
        println(i)
    }
}

左闭右开

until

val range 0 until 10

步长

step

fun circulation1(){
    //val range=0 until 10
    for (i in 0 until 10 step 2){
        println(i)
    }
}

downTo

fun circulation2(){
    for (i in 10 downTo 0){
        println(i)
    }
}

q(≧▽≦q):Kotlin新特性

1. for-in无法实现特殊场景,可以改用while