Java JITs definitely do have type feedback. They profile the types of objects at virtual call sites and do guarded inlining, as well as removing expensive interface casts, etc. The JVM doesn't really have a distinction between classes generated on the fly and those that were on disk, as they all go through a classloader anyway. JVMs, for the most part, blow their brains out at the end of the day and start with zero the next VM run.