How do I make sure only one instance of my program can be executed?

Question

I want my program, a Java executable .jar, to be run just once. I made a program but now I want users not to be able to open more than one instance ....thanks for your time.

Answer 1

Java Web Start can handle this in a platform independent way, but you will need to let your program be started by Java Web Start which requires some tinkering.

See http://download.java.net/jdk7/docs/technotes/guides/javaws/developersguide/examples.html#SingleInstanceService for how to let a single instance handle multiple "start me" requests.