Java is excellent as it just works on so many platforms. My Java software is used on Windows, Linux & Mac. Mac users will notice that the behaviour of Java applications doesn't follow that of the native applications (unlike on Windows/Linux). This is a bit annoying to be honest, however, there are several steps you can take to give a more Mac "feel" to your application.
This
link was recently forwarded to me, some of it is certainly useful, although some outdated, but it will give you an idea of what you can alter to add that Mac feel.