@Override
    protected BasePartitionEvaluator createPartitionEvaluator(
        WindowFrameDef winFrame,
        PTFPartition partition,
        List<PTFExpressionDef> parameters,
        ObjectInspector outputOI,
        boolean nullsLast) {
      return new BasePartitionEvaluator.SumPartitionDoubleEvaluator(this, winFrame, partition,
          parameters, outputOI, nullsLast);
    }
class for storing double sum value.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFSum.java