code: public List<ColumnType> getColumnTypes() {
          List<ColumnType> list = new ArrayList<>(columnMetaData.size());
          for (ColumnMetaData md : columnMetaData)
              list.add(md.getColumnType());
          return list;
      }
docs: A copy of the list of {@link ColumnType}
  for this schema
  @return the list of column  types in order based
  on column index for this schema