The method seems to be building a String using concatenation in a loop. In each iteration, the String is converted to a StringBuffer/StringBuilder, appended to, and converted back to a String. This can lead to a cost quadratic in the number of iterations, as the growing string is recopied in each iteration.
Better performance can be obtained by using a StringBuffer (or StringBuilder in Java 1.5) explicitly.
For example:
// This is bad String s = ""; for (int i = 0; i < field.length; ++i) { s = s + field[i]; } // This is better StringBuffer buf = new StringBuffer(); for (int i = 0; i < field.length; ++i) { buf.append(field[i]); } String s = buf.toString();
This rule is deprecated, use {rule:squid:S1643} instead.