public Comparator<VectorHashKeyWrapperBase> getComparator(String columnSortOrder, String nullOrder) {
    VectorHashKeyWrapperGeneralComparator comparator =
            new VectorHashKeyWrapperGeneralComparator(columnVectorTypes.length);
    for (int i = 0; i < columnVectorTypes.length; ++i) {
      final int columnTypeSpecificIndex = columnTypeSpecificIndices[i];
      ColumnVector.Type columnVectorType = columnVectorTypes[i];
      comparator.addColumnComparator(
              i, columnTypeSpecificIndex, columnVectorType, columnSortOrder.charAt(i), nullOrder.charAt(i));
    }
    if (comparator.getComparators().length == 1) { // don't use the composite comparator for n=1
      return comparator.getComparators()[0];
    }
    return comparator;
  }
Get the row-mode writable object value of a key from a key wrapper
@param keyOutputWriter
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/wrapper/VectorHashKeyWrapperBatch.java