code: public int getDescent(String text) {
          int min = 0;
          char chars[] = text.toCharArray();
          for (int k = 0; k < chars.length; ++k) {
              int bbox[] = getCharBBox(chars[k]);
              if (bbox != null && bbox[1] < min)
                  min = bbox[1];
          }
          return min;
      }
docs: Gets the descent of a <CODE>String</CODE> in normalized 1000 units. The descent will always be
  less than or equal to zero even if all the characters have an higher descent.
  @param text the <CODE>String</CODE> to get the descent of
  @return the descent in normalized 1000 units