Need help with Executable Jar Icons

Hi all,

I have this executable Jar file that I have recently made. I've looked around the net and managed to find many tutorials on how to change the icons of files, programs, etc.

But I want to change the icon that shows on the dock upon launch. Some tutorials have you drag the app to the dock and it will show the new icon, but what if I didn't want to drag this particular executable to the dock, or what if I wanted to give this file to a friend who doesn't have it customised?

Thanks in advance