Problems in storing data in a H5 file?

double val = 18.5;

                            ByteArrayOutputStream bytestream = new ByteArrayOutputStream();

                            DataOutputStream datastream = new DataOutputStream(bytestream);

                            datastream.writeDouble(val);

                            datastream.flush();

                            datastream.close();

                            bytestream.close();

                            byte[] bytes = bytestream.toByteArray();

                            for (int j = 0; j < bytes.length; j++) {

                            write_data[indx] = bytes[j];

                            indx++;





H5.H5Dwrite(dataset_id, memtype_id, HDF5Constants.H5S_ALL,

                            HDF5Constants.H5S_ALL, HDF5Constants.H5P_DEFAULT,write_data);