For the last few days I’ve been working on an Eclipse plug-in using a combination of mixed Java/Scala projects. That is, the same source folder contains both Java and Scala files. I think it’s awesome that this is finally working! At least I wasn’t aware if it was working before. There are still bugs in the Scala Plug-in for Eclipse, but the integration with JDT is now a lot better than before, thanks in part to Equinox Aspects as I understand. You can get the 2.8.x branch of the Scala plug-in, which contains the improvements, from the nightly builds update site.
Also, I noticed a curiosity: I wrote the most complex parts of the mixed projects in Scala, but I mostly created bugs in the comparatively trivial Java code. The Scala code ended up almost bug free from the start, even with hours and hours of coding without actually running the code. Is it really harder to create bugs in Scala? I’d like to think so.