Java or C++ ? which one is more useful?

Answer 1

to be frank with you c++ is more useful than java and it's faster than java because it's is next to system language and it is rarely used in conventionally programming. It it next to machine language so it is very very fast.
You can not use Java to develop hardware drivers.

Answer 2

It depends of your objective, if you seek to build mobile apps, Java is more usefull. But if your objective is to create bigger programs, games or OS, than C++ is more usefull to you.

Answer 3

both

Answer 4

Can i write something about Linux with any of C's ?

Answer 5

nothing more useful than others. the useful one is your skill to craft the code whatever the language are.