I'm learning Java in my spare time just because in the same sense it pays to know C if you dig Unix, I suspect it pays to know Java if you dig the JVM.

The language has not proved to be too disturbing, happily, but I'm finding the tooling and ecosystem to be rather arcane and difficult to get a grip on at first. Build tools, a choice of JVMs and JDKs, "enterprise" this or that.. it seems all the stuff around the language is the real minefield than the relatively simplistic language itself.