Comment by cess11

"In theory, you could pick up your one language, say, Java, and through the course of a normal career learn everything necessary to program in that language in the best possible way."

OK, then you know about currying, immutable data structures, map/reduce/filter, &c.

Because Java has that since way back when. No real closures, I think, but that doesn't matter much because the anonymous functions do what you want pretty much all the time and you could probably invent your own closures if you really want something else.