I'm confused by TotalNumOfLettersGenericUDAF.TotalNumOfLettersEvaluator.reset

[ylyhlh]

Thanks a lot for the great tutorial about UDF and UDAF, they are awesome and extremely helpful!
But I got a little confused by TotalNumOfLettersGenericUDAF.TotalNumOfLettersEvaluator.reset function

Original it is, looks like nothing did here:

    public void reset(AggregationBuffer agg) throws HiveException {
        LetterSumAgg myagg = new LetterSumAgg();
    }

In my view it should look like this:

    public void reset(AggregationBuffer agg) throws HiveException {
        ((LetterSumAgg)agg).sum = 0;
    }

Maybe I'm wrong, if so can you tell me what did the reset function should do here,