[andr]

To answer your question, Java is very easy to reverse engineer. Google for a decompiler. Several years ago I would get an almost perfect copy of the original source, with the proper variable names, etc. The only thing missing were comments :)

The legality of you reverse engineering the software is a different matter. But if you have paid the $2500 in question, then you own it.

[kragen]

Whether you own the software or not depends on what the contract says. It is entirely legal to sign a contract to perform a service for somebody for some amount of money without assigning them copyright in the results.