Can't we say: system.out.printIn(sum(5,2)); instead of assigning sum(5,2) to x?

Answer 1

yes

Answer 2

Sure, you can... But keep in mind that you quickly lost much readability in your source code, without real improvments ^^ ( this kind of are only necessary on low memory system, or low speed if speed is a necessity )

Answer 3

yes, it's possible