What is output of "hi"+""+"hello"

Answer 1

You have 3 strings:
The first contains the 'hi'
The second contains nothing
The third contains 'hello'
In this case, the second is not useful, but it can be if you add a space or a coma like:
"hi" + " " + "hello": hi hello
"hi" + ", " + "hello": hi, hello

Answer 2

hihello

Answer 3

No use

Answer 4

Initialize an empty String using

String s="";

Convert other types easily to String by adding ""

String s = 15 + "";

Answer 5

Then what is use of ""