Kotlin by Example: Casts

Kotlin supports different types of casts.	fun withCast(x: Any) {
This is a normal cast using the `as` operator, which will throw an exception when `x` is not of the `String` type.	val xstr = x as String println("x has length ${xstr.length}") } fun withSafeCast(y: Any) {
This is a safe cast, using the `as?` operator. This will return `null` when `y` is not of the `String` type.	val ystr = y as? String if (ystr != null) { println("y has length ${ystr.length}") } } fun withSmartCast(z: Any) {
Kotlin also has a feature called smart casts, which use the `is` operator.	if (z is String) {
Inside this `if` block, the compiler has determined that `z` has type `String`.	println("z is a string with length ${z.length}") }
Smart casts also work when the `is` operator is negated.	if (z !is String) { println("z is not a string") return } println("Yes, z is a string with length ${z.length}") } fun main() { val x1 = "hello, world" val x2 = 1.0 withSmartCast(x1) withSmartCast(x2) withSafeCast(x1) withSafeCast(x2) withCast(x1) withCast(x2) }

$ kotlinc main.kt -include-runtime -d main.jar

$ java -jar Main.jar

z is a string with length 12

Yes, z is a string with length 12

z is not a string

y has length 12

x has length 12

Exception in thread "main" java.lang.ClassCastException:

class java.lang.Double cannot be cast to class java.lang.

String (java.lang.Double and java.lang.String are in modu

le java.base of loader 'bootstrap')

        at MainKt.withCast(main.kt:6)

        at MainKt.main(main.kt:49)

        at MainKt.main(main.kt)