@VisibleForTesting
  void init(List<String> typeNames) throws HiveException {

    final int count = typeNames.size();
    allocateArrays(count);

    for (int i = 0; i < count; i++) {
      initEntry(i, i, TypeInfoUtils.getTypeInfoFromTypeString(typeNames.get(i)));
    }
  }
This class extracts specified VectorizedRowBatch row columns into writables.

The caller provides the data types and projection column numbers of a subset of the columns
to extract.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorExtractRow.java