My biggest concern is that i will get a good job(after college) with some big firm and hes going to say, "ok, but can u write java?"

i wanna be able to say YES but if he needs me for java not c++ then that job would be a waste of my time. But i want to know both so i'm flexible, so what i am thinking is Java a slow learn language or could i pick it up in a few days(or weeks) should i need it at a job?