I don't know how java deals with this but on posix platforms a sub-process holds some resources that have to be claimed back by the parent process. This includes (but is not restricted to) the result of the process, i.e. its return value. In case you are familiar with (posix) threads: there you have to join a thread after it terminated. It's conceptually the same thing here.

If you find yourself joining posix's threads only for this reason you should consider setting the detachstate attribute to PTHREAD_CREATE_DETACHED instead. Glen