@Override
  public boolean matches(String name, ColumnVector.Type inputColVectorType,
      ColumnVector.Type outputColVectorType, Mode mode) {

    /*
     * Count input and output are LONG.
     *
     * Just modes (PARTIAL2, FINAL).
     */
    return
        name.equals("count") &&
        inputColVectorType == ColumnVector.Type.LONG &&
        outputColVectorType == ColumnVector.Type.LONG &&
        (mode == Mode.PARTIAL2 || mode == Mode.FINAL);
  }
class for storing the current aggregate value.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFCountMerge.java