Declaring variables inside or outside of a loop

Question

Why does the following work fine?

String str;
while (condition) {
    str = calculateStr();
    .....
}

But this one is said to be dangerou

Answer 1

If you don't need to use the str after the while loop (scope related) then the second condition i.e.

  while(condition){
        String str = calculateStr();
        .....
    }

is better since if you define an object on the stack only if the condition is true. I.e. use it if you need it