Implement 'Maybe' in Java

Question

Guava's Optional class comes dangerously close to being a useful Maybe type in Java. All I want to do is extend it a bit:

class Maybe<X> extends Optional<X> {
  public Maybe<Y> map(Function<X, Y> f) {
    if (isPresent()) {
      return Maybe.of(f.apply(get()));
    }
    return Maybe.absent();
  }
}

Is that so hard? Apparently yes, it is. Java has no idea what the Y type is in the map function, and everything dies horribly. Is it possible to write a generic map in Java?

Answer 1

You're looking for Optional.transform(Function), following Guava's convention of calling all map-style functions "transform" (e.g. Lists.transform, Iterables.transform, etc).

Answer 2

This is, as of JDK8, implemented as java.util.Optional, and it seems to have the mapping function that you're looking for as it integrates with Streams. Here is the documentation.

I know this reply is quite late, but I'm adding it as an answer for the benefit of others searching for this.