Why is

String.toInt()

just an alias for

parseInt()

, but

String.toIntOrNull()

is custom implementation instead of trycatch implementation of parseInt()? Is it because throwing exceptions in java is heavy or something like that?

Yes, this is because of a Throwable that will be created but ignored

To extend a bit on that, every time* a Throwable is created, it captures the current stack trace, which is pretty costly, and throwing and catching across function boundaries also has some overhead. *actually not every time, see this stackoverflow answer: https://stackoverflow.com/a/36344265/3887813