I have a similar answer to the one I gave when I apparently misunderstood your question the previous time you asked:
(on rereading that thread, I don't know why I thought you wanted the calling program's own pid.)
But instead of /proc/self use /proc/PID
with the numeric pid of the process you want.
You can read files with ordinary java, so you don't need any native methods, external programs or special API. Of course the results will be fairly OS specific, but I expect any method of getting process status would give OS specific results.