As a frontend dev I think this is where I'm legally obligated to make the "java sucks" joke. So, there you go.

On the opposite end, I still wouldn't touch it with a 10 foot pole because I despise that object oriented nonsense, but honestly pick a project you already know inside out. Something that YOU enjoy. Whether that's some frontend shit, some script you use regularly, whatever. Then, rewrite that in java. You already know exactly how it should work, so all you need to focus on is the syntax, build system, libraries, etc.

It's my absolute favorite way to get started on writing things in a new language. Of course, I would never traumatize myself by doing it in Java, but the same principle applies even for those who enjoy self flaggelation.

Ok, I think that's my quota of "java bad" comments for the day.

Now, for real, go rewrite something you're already intimately familiar with in Java and thank me later.

I'm gonna go screw with Haskell some more now. Have fun.