How to convert an Optional to an OptionalInt?

Question

I have an Optional that I want to \"convert\" to an OptionalInt, but there doesn\'t seem to be a simple way to do this.

Here\'s what I want

Answer 1

If you have any object and not just a String, you can temporarily go through a Stream:

public static  OptionalInt toOptionalInt(Optional optional, ToIntFunction func) {
  return optional.map(Stream::of).orElseGet(Stream::empty)
    .mapToInt(func)
    .findFirst();
}

This solution has the advantage to be a one-liner, meaning you can copy/paste the content of the method and just change func to whatever you want. The disadvantage is going through a Stream to achieve what you want. But if you want a generic one-liner, this is it.

If you want a utility method, you probably prefer to use the following:

public static  OptionalInt toOptionalInt(Optional optional, ToIntFunction func) {
  if (optional.isPresent()) {
    return OptionalInt.of(func.applyAsInt(optional.get()));
  } else {
    return OptionalInt.empty();
  }
}