You have done the right thing, 'first do no harm' don't delete, send virus to the chest and investigate as you have.
In this case there is little problem as actually deleting the contents of the JAVA cache shouldn't be an issue. However I would suggest that you send these files for further analysis by avast as possible false positives as they are [Heur]istic detections.
Open the avast Chest, avastUI, Maintenance, Avast Chest, Right click on the file/s and select 'Submit to virus lab...' complete the form and submit, the file will be uploaded during the next update.
Periodically check it (scan it in the chest), if it is no longer detected then you can assume it was an FP. It is is detected after a couple of weeks you can assume it was a good detection and delete it from the Chest.
- Next I would ensure that you have the latest JAVA version as that is essential. I would also suggest a visit to this site, which scans your system for out of date programs that have patches to close vulnerabilities,
http://secunia.com/software_inspector/.