static HiveVarcharWritable nextVarchar(ColumnVector vector,
                                         int row,
                                         int size,
                                         Object previous) {
    if (vector.isRepeating) {
      row = 0;
    }
    if (vector.noNulls || !vector.isNull[row]) {
      HiveVarcharWritable result;
      if (previous == null || previous.getClass() != HiveVarcharWritable.class) {
        result = new HiveVarcharWritable();
      } else {
        result = (HiveVarcharWritable) previous;
      }
      BytesColumnVector bytes = (BytesColumnVector) vector;
      result.set(bytes.toString(row), size);
      return result;
    } else {
      return null;
    }
  }
If the current batch is empty, get a new one.
@return true if we have rows available.
@throws IOException
ql/src/java/org/apache/hadoop/hive/ql/io/orc/RecordReaderImpl.java