I'm not a full time Java developer, but unless you have a really hard time adjusting to the syntactic differences or will grumble when you do something you know

I'm not a full time Java developer, but unless you have a really hard time adjusting to the syntactic differences or will grumble when you do something you know would be "so much easier in X", you should be fine. You'll learn the JVM, APIs, and libraries you'll need to be a Java programmer. That seems like a win to me.