Hi @benji , great you have enthusiasm for beautiful UI/UX. There are 3 kinds developer you can become. 1. Front-End Developer 2. Back End Developer and 3 Full Stack Developer.
Now, "front-end" means what you see, primarily on the browser. User Interaction, fonts, images, color and lots more. How and where they appear.
"Back-end" means data Interaction. Fonts, images, color and lots more are all data stored on a server somewhere. Back end programming enables you call these "data" so that they can be displayed by your browser.
Full Stack means combination of both front-end and back-end. So you are a full stack developer if you know front-end and back-end development.
Java is back-end development. (Mind you that Java and JavaSript have no relation. They are basically different languages just as english is not french). It will be great to know Java, but really, you want to start with how it looks since you like UI/UX.
Hope this helps. Best Regards.