when

fun getColor(color :Color){
    when(color){
        Color.BLUE -> println("this is blue")
        Color.RED -> println("this is RED")
        Color.GREEN -> println("this is GREEN")
        Color.BLUE2 ,Color.RED2 -> println("this is blue or red")
    }
}
// main 调用
getColor(Color.GREEN)

is

  fun GetNumber(x: Any) = when (x) {//kotlin中所有类都有一个共同的父类： Any
        is String -> {//如果x是String类型，执行该代码块
        }
        is Int -> {
            //如果x是Int类型，执行该代码块
        }
        else -> false
    }

javaClass

var args:Int =3
println(args.javaClass)
println(args::class.java)
输出
int
int