code: public double getValueAsDouble(int index) throws IOException {
          if (index >= structure.valueSizes.size()) {
              throw new IOException("Index " + index + " is out of range.");
          }
          return Bytes.toDouble(value, structure.valueByteOffsets.get(index));
      }
docs: Returns the value belonging to the given field as long
  
  @param index
  the index of the requested field
  @return the requested value
  @throws IOException