It is a bug. I was wondering why no one download user uploaded jar files in the last week.
I just modified the code. You should be able to download it now.
I though you have did similar work before.
May be you can check out [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=806]Integrator y= ? f(x) dx[/url]
You can drag the blue dot, which is follow the curve of of the function (user can input different function).
And the red curve is the integal of the function.