Java - Fastest way to check the size of String

Question

I have the following code inside a loop statement.
In the loop, strings are appended to sb(StringBuilder) and checked whether the size of sb has reached 5MB.

Answer 1

If you loop 1000 times, you will generate 1000String, then convert into "UTF-8 Byte" array, to get the length.

I would reduce the conversion by storing the first length. Then, on each loop, get the length of the added value only, then this is just an addition.

int length = sb.toString().getBytes("UTF-8").length;
for(String s : list){
    sb.append(s);
    length += s.getBytes("UTF-8").length;
    if(...){
    ...
    }
}

This would reduce the memory used and the conversion cost