The fact that Java source and comment is used in UML - Java roundtrip tools as more or less interchangeable things is completely in line with the OMG MOF model whre UML and Java are both a M2 level definition. This means, if I'm not mistaken that one could use Java as a basis for code generation instead of UML.
This would be good news since UML is still very bothersome when entering large amounts of information. At least I have found very few UML modelling tools if any at all where one could enter information as effectively as in an IDE. I had good hopes for HUTN (Human Usable UML) but I agree with my neighbour that it probaby is easier to use a syntaxt one is familiar with.
Mapping Java to UML instead of the other way around seems a problem, but one probably doesn't need to be able to express all UML features using Java to end up with a powerfull basis for codegeneration based on MDA principles.
These are exciting times indeed.