Note that what OP said he found was a JAR, not code. If you found an executable built in any language, I would expect it to still be able to run 13 years later.
JAR is not executable, it's a zip-archived bytecode (basically the same code with better readability for machines, very easy to decompile back to sources, you usually only lose comments and whitespaces). Java is an interpreted language, not compiled, at least mainstream VMs.