JBullet supports “custom shapes” which can be implemented in Java. I believe that native does not support this. I guess to do the same with Bullet, it would need to have callbacks into Java code via JNI. The overhead of doing that for those purposes seem like it’d be pointless.
There was an old project posted here which used JBullet that “broke” once native Bullet was introduced, due to it relying on custom shapes. I’m not sure if it was fixable or not, but the author didn’t seem to think it would be easy (or possible) when I inquired.
I’m going off old memory and I’m not well versed in Bullet integration so I could be mistaken here.
Ah, found the project:
For the record though, I don’t use JBullet for anything currently, only native. I’m just not a fan of losing options, unless it’s really necessary. I’m sure there are some use cases where JBullet works out better, and some where native does…
Edit: Ha! I just fired that up in JME 3.2, after some shader config fixes, it still works. With JBullet, though.