I need a directory to store application data.
of course this will be different on Windows, Mac, or Linux.
i think these are the best directorys for this
for windows i need
[current user directory]/AppData/Local
on OS X i need
[current user directory]/Library/Application Support
detect the platform!!
System.getProperty("os.name")
--- Update ---
and you need the username too
String username = System.getProperty("user.name");