What is the use of StringBuilder in java

Question

Is it mandatory to use StringBuilder for string concatenation in java? Is it so?

Answer 1

If you use String concatenation in a loop, like

String str = "";
for (int i = 0; i < 50; i++)

{
    str += ", " + i;
}

then StringBuilder is used (not StringBuffer) instead of a String because it is much faster and consumes less memory.

If you have a single statement,

String str = "1, " + "2, " + "3, " + "4," + "5, " ...;

then you can use Strings because the compiler will use StringBuilder automatically.