code: public long getFieldAsLong(int tag, int index) {
          Integer i = (Integer)fieldIndex.get(Integer.valueOf(tag));
          return fields[i.intValue()].getAsLong(index);
      }
docs: Returns the value of a particular index of a given tag as a
  long.  The caller is responsible for ensuring that the tag is
  present and has type TIFF_BYTE, TIFF_SBYTE, TIFF_UNDEFINED,
  TIFF_SHORT, TIFF_SSHORT, TIFF_SLONG or TIFF_LONG.