Java itself is pretty fast and wonderful, at-least the modern versions. It’s the libraries and the ecosystem. Java folks typically over engineered things with layers and layers of abstraction in the name of “enterprise”.

Writing a web app in Django/express vs tomcat/jboss you’d feel the pain. It would take forever to start, chew an insane amount of memory and nodejs runs circles around it.

There aren’t that many things where Java is a great usecase. If you want serious perf, then you’d go C/C++/rust. Perf with nicer abstractions would be Go. Dynamic languages? Javascript and Python.

Yes Android uses Java heavily but even Google got sued left and right by Google. Oracle simply gives Java a really bad rep.

Java is still heavily used by banks and enterprisy companies but I’d bet C# has equal penetration. C# is just designed much nicer, it’s like java but a great user experience and similar perf. With .NET being OS, i’d bet on C# to have bright future. MS invests a lot more into it than Oracle into Java.

So to answer your question if you should learn Java. Absolutely go build a simple Android app or a simple cli app. I wouldn’t count on it being the only tool in the toolbox.

If you have limited time and you want to make a choice on what to learn. I’d say Javascript and Python. Those are in good demand nowadays.