@SuppressWarnings("unchecked")
  public void read(MapJoinObjectSerDeContext context, Writable currentValue) throws SerDeException {
    AbstractSerDe serde = context.getSerDe();
    List<Object> value = (List<Object>)ObjectInspectorUtils.copyToStandardObject(serde.deserialize(currentValue),
        serde.getObjectInspector(), ObjectInspectorCopyOption.WRITABLE);
    if(value == null) {
      addRow(toList(EMPTY_OBJECT_ARRAY));
    } else {
      Object[] valuesArray = value.toArray();
      if (context.hasFilterTag()) {
        aliasFilter &= ((ShortWritable)valuesArray[valuesArray.length - 1]).get();
      }
      addRow(toList(valuesArray));
    }
  }
Remove all elements in the RowContainer.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinEagerRowContainer.java