Do you want somebody to write your code for you: why? I mean, why would they, but also why would you want them to. The whole thing seems pointless.
Note: it might be argued that empty sets don't have sums, so the best solution to your problem is to generate a set containing the first element from your given set ... twice.
[Edit] Also, an answer was given to you when you hijacked this thread: http://forum.java.sun.com/thread.jspa?threadID=5113852&messageID=9670715#9670715