For java programming, you can add thread to ask java run some job continuously. It is a standard java programing method, you should be able to find out how it can be done with any java programming books (or online tutorial).
I have created this program almost 10 years ago with JDK1.0.2
May be there are better way to do it. If you need java programing help. please check out other related web site.
If you need help in physics, I will try to help. But I do not have time to read how it can be done with latest java. I use EJS to create new simulations since 2001. EJS is a tool which I do not need to know much about java programming, I just need to concentrate on the physics model. So if you are interested in java programming, you should ask some other expert. If you just want to create scientific java simulation without too much programming skill. I would suggest you use EJS.
You can find latest information about EJS from http://fem.um.es/EjsWiki