[foobarchu]

I hit this just recently with an in-house dependency injection library. We upgraded the version in an application, it worked great, we deployed it to a cloud environment. Lo and behold the application wouldn't start up, and more importantly wouldn't give us a real reason why. In the end I discerned from cryptic logs that it was because Java had loaded up both the jar of the version we wanted and the jar of an older version that happened to be in the classpath too. You can't have two dependency injection systems running at the same time, so they fought and came to a stalemate. Deleted the bad version and it was all good.

I know that this isn't entirely Java's fault, as that second jar shouldn't have been there to begin with, but it's pretty ridiculous that two versions of the same dependency can be loaded and in use at the same time.