if
Kotlin的if有返回值，返回值就是执行分支的最后一个表达式
val max = if (a > b) a else b
val max = if (a > b) {
print("Choose a")
a
} else {
print("Choose b")
b
}
when
when类似于switch, 如果是当做一个赋值语句的一部分，else是必须的
when (x) {
1 -> print("x == 1")
2 -> print("x == 2")
else -> { // Note the block
print("x is neither 1 nor 2")
}
}
条件可以写在一起
when (x) {
0, 1 -> print("x == 0 or x == 1")
else -> print("otherwise")
}
函数返回值当作条件
when (x) {
parseInt(s) -> print("s encodes x")
else -> print("s does not encode x")
}
range当作条件
when (x) {
in 1..10 -> print("x is in the range")
in validNumbers -> print("x is valid")
!in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}
is成立后会将变量自动转型：
val hasPrefix = when(x) {
is String -> x.startsWith("prefix")
else -> false
}
当when不带参数时，类似于if，会执行true后面的语句
when {
x.isOdd() -> print("x is odd")
x.isEven() -> print("x is even")
else -> print("x is funny")
}
for
for 用来遍历定义了iterator()的对象，iterator返回的东西：
- 有
next()方法 -
hasNext()return 布尔值
for 还可以用来遍历具有index的对象
for (i in array.indices) {
print(array[i])
}
for ((index, value) in array.withIndex()) {
println("the element at $index is $value")
}
while
while和do..while和Java一样
