Can i learn java by own without joining classes

Yes

You can build a rocket by yourself if you're persistent enough.

Most definitely

This is the industry of self improvement and self education. There's enough resources online in book, tutorials, or video style to gain enough knowledge quickly.

Some people can but I don't know about you. But I don't know if joining classes would change that.

P.S. Not like that flat earth guy.

No you have to join class since java is object oriented.

yes but C++ is supported on more platforms

I'd say yes but one advantage I felt at uni was that in class they taught us programming rather than a programming language. So it never mattered which language we were using as we used different languages in different courses. As long as you understood the paradigms it was just a question about getting used to the syntax

Of course.

@PublicByte well as long as you use it correctly its fine, no all that study it can use it well. Some areas are more or less easy to study yourself