/** Return next string in the sequence "a", "b", ... "z", "aa", "ab", ... */
static String getNextDirName(String old) {
StringBuilder sb = new StringBuilder(old);
// go through and increment the first non-'z' char
// counts back from the last char, so 'aa'->'ab', not 'ba'
for (int ii = sb.length() - 1; ii >= 0; ii--) {
char curChar = sb.charAt(ii);
if (curChar < 'z') {
sb.setCharAt(ii, (char) (curChar + 1));
return sb.toString();
}
sb.setCharAt(ii, 'a');
}
sb.insert(0, 'a');
return sb.toString();
}
