How to use scala.None from Java code

Question

Possible Duplicate:
Accessing scala.None from Java

In Java you can create an instance of Some using the constructor, i.e. new Some(value), but None has no partner class. How do you pass None to a Scala function from Java?

Answer 1

The scala.None$.MODULE$ thing doesn't always typecheck, for example this doesn't compile:

scala.Option<String> x = scala.None$.MODULE$;

because javac doesn't know about Scala's declaration-site variance, so you get:

J.java:3: incompatible types
found   : scala.None$
required: scala.Option<java.lang.String>
    scala.Option<String> x = scala.None$.MODULE$ ;

This does compile, though:

scala.Option<String> x = scala.Option.apply(null);

so that's a different way to get a None that is usable in more situations.