Qt and Java can do cross platform software, however it's not possible to make a UI that's usable on desktop, tablet and mobile. You will end up creating separate apps.
Qt is actually really impressive in my opinion, it's possible to recompile a desktop software for mobile, sometimes without any code change at all.
Qt is actually really impressive in my opinion, it's possible to recompile a desktop software for mobile, sometimes without any code change at all.