presto-main/src/main/java/io/prestosql/operator/aggregation/state/DigestAndPercentileStateFactory.java/DigestAndPercentileStateFactory/getSingleStateClass
class DigestAndPercentileStateFactory:    @Override
    public Class<? extends DigestAndPercentileState> getSingleStateClass()
    {
        return SingleDigestAndPercentileState.class;
    }