Java kinda sucks dick for game dev tbhwy. I've never played with it, but the only real game library for Java is
libGDX. To distribute it to desktop users, best way would probably be to distribute it through a burner github hosting or filedrop, and distribute the game JAR bundled with a JRE, as outlined in their documentation:
JAR,
JRE
though tbqh, most brothermen are phoneposting boomers, so if you want the game to be played, a browser based/web deployable game is the way to go, since then brothermen don't need to install shit either. Unity can be compiled into
a webGL easily, and deployed for free to simmer.io or itch.io and link people to the URL to play in browser on desktop/laptop, and without any real changes to the codebase cross-compile to an android SDK and share that if people want to install and play it on android mobile. iOS app installation would require too much fuckin red-tape, so probs not worth it, but it can be done as well in Unity. Also, tons of documentation for all this stuff in Unity, along with lots and lots of free assets to use.
If you want to play with Java, I'd say use Springboot on Heroku free hosting to create the backend and template for a site that will host the game, then use some javascript game libraries like PhaseJS to develop the game in the web front-end with JS, HTML, and CSS. Then use the springboot part to save scores to a database or some other CRUD operations.
Java is 'simpler' than C# in some ways, there's less random weird shit than C# overall. I found it's easier to go from C# => Java than the opposite. Java at its core is pretty pure OOP. If you want to brush up on OOP concepts, just pirate some good Java book PDFs from one of the github projects where a pajeet has just dumped lots of them.
Mostly, get a hang of the syntax and DS of the language. Any further refinement will depend on what your job entails, what frameworks your job uses, what the CICD pipeline is like (if there hopefully is one), and lots of shit that is usually different from company to company and team to team.
Other random unsolicited tips (assuming you're newer to the field...):
Figure out what editor or IDE you prefer and get it set to your liking. If your company will comp for Jetbrains, I really like VS with resharper for C# and IntelliJ for Java. If your company won't comp and you still have a university email you can access, you can lie and get a student license for their shit for free for a couple years. If nothing else, it lets you install it on your personal computer to fuck around. Their shit has a lot of QoL features for compiling and managing a project, so it takes some of the pain out of it.
It will also let you get some of the awkward kinks of getting a working env set up on your own time before you start the new job so that you look smooth and confident when you start and get your work env configed quick.
If you know (or can figure out) what testing and CICD pipeline your company uses (jenkins, github actions, etc.) ahead of time, read docs and fuck around with it. They can be janky as fuck and a massive pain in the ass to deal with for deployment, so if you can get ahead of it before you join, you'll endear the Senior SWEs to you by not needing as much help. Same thing for containerization, esp. if they're not using Docker/K8s.
Hopefully you're going FAANG, since they'll cover most/all of this shit in your induction cycle training camp weeks, assuming you're coming in at a more entry level SWE role. If it's a smaller company, it'll vary a lot and depend mostly on how well your team keeps shit organized and documented centrally.
A random slack with your question in the first message upfront will make you way more liked by fellow SWEs than the pajeet "hello good morning" and waiting for a response, or the PM "can I call?" horseshit.
Avoid calls. Emails and slack messages give you documentation of what you said and did, and also act like documentation when you're trying to remember some random server migration address remapping shit that happened over a year ago and wasn't centrally documented. Also helps when people try to claim you said or promised something you didn't. If they force a call or a meeting, send an email afterwards recapping what you said and/or promised in the meeting to them. People in this industry will try to motherfuck you and its oftentimes when you least expect it.
Don't let the PMs and POs fuck with your head about your velocity. Lots of them (depending on the company) will play head games to try to push velocity to stupid unmaintainable levels. Don't burn yourself because it will never be enough for those types. Unless your actually getting PIPed, its probably headgames. And if you're at Amazon and you get PIPed, just remember that they pride themselves on their 30% churn rate and use the A on your resume to leapfrog to somewhere better. ALso, don't join AWS or any AWS team under any circumstance.
That's all I got brotherman. C# is gay, but it's used in lots of useful things and microsoft's documentation is usually pfg. Java is simple and really easy to get a grasp on if you understand the concepts of OOP. It's the frameworks and libraries that turn it into a fuckin mess. Enjoy.