With respect to being open source - it’s GPL licensed (with classpath exception), and there are several vendor-supported builds of the JDK. People typically use these or OpenJDK. You only run into licensing trouble if you use the gratis, commercial build of Java provided by Oracle, which you would only do if you’re a newbie or have a highly unusual usecase (there’s really no other reason to use it, even in industry).
Java has a massive ecosystem which has the benefit of having both extremely stable, old libraries and newer stuff. It’s the language of industry and middleware; it’s verbose (but less so in recent versions); it’s reliable and easy to reason about. Its strong/static/declared typing is something that some people don’t get around, which is fine for them but really it’s just nice for sanity when working with a code base that’s more than a few thousand lines or that someone else wrote.
I reckon it’s the Corolla of programming languages. For what it’s worth I think it’s also pretty fast, even though its zero-to-sixty might not be very impressive.
