I agree. Typing just "java -server" gives a usage message. In fact, typing "java -xyz", where xyz is any valid
Java option, also gives an error. In fact, typing just "java" gives the same error. Typing nothing (by just pressing Enter) doesn't give an error for me. Does it for you?
Anyway, note that this usage message starts
Usage: java [-options] class [args...]
which should give you a clue as to this "error" message.
If you're getting a
different error message, you might share it with us.