docs: public static String replaceNonAlphanumeric(final String str, final char subst) {
          final StringBuffer ret = new StringBuffer(str.length());
          final char[] testChars = str.toCharArray();
          for (final char testChar : testChars) {
              if (Character.isLetterOrDigit(testChar)) {
                  ret.append(testChar);
              } else {
                  ret.append(subst);
              }
          }
          return ret.toString();
      }