How to convert Int to Hex String in Kotlin?

You can still use the Java conversion by calling the static function on java.lang.Integer:

val hexString = java.lang.Integer.toHexString(i)

And, starting with Kotlin 1.1, there is a function in the Kotlin standard library that does the conversion, too:

fun Int.toString(radix: Int): String

Returns a string representation of this Int value in the specified radix.

Note, however, that this will still be different from Integer.toHexString(), because the latter performs the unsigned conversion:

println((-50).toString(16)) // -32
println(Integer.toHexString(-50)) // ffffffce

But with experimental Kotlin unsigned types, it is now possible to get the same result from negative number unsigned conversion as with Integer.toHexString(-50):

println((-50).toUInt().toString(16)) // ffffffce