How to detect that my aplication is running?

I think about something.
When my aplication is running, then if user click its icon on desktop, it will create another instance of my application. So there are two of my aplication running on the machine.

What i want is: when user click its icon on desktop, it will just show the application that has been running instead of creating new process.

How to do that???
regards,

---

I'm Okie Eko Wardoyo Owner of http://www.mediatutorial.web.id