That's maybe the one most important problem arising with Java if you are using it in an environment you do not know or not know well (as it is, on client machines - especially using Java on the web).
As of it, using Java 7 features in Web pages - no way, maybe no way ever if you do not want to exclude a big mass of people out there on the market.
People still write client side Java? shudder I love Java, but good god would I never write an Applet again.
So I guess I'll be able to use closures the moment I can stop trying to make my web pages work in IE 6: in the yeat 2040