Compound

CompoundAggregate 实现了“复合聚合”：即多个聚合的组合。（请注意，这可以在一次遍历中计算多个聚合。）

类定义

    public static class CompoundAggregate implements Aggregate
    {
        public void initialize(Object val) 
        {
            for (Aggregate agg : aggregates) 
            {
                agg.initialize(val);
            }
        }
 
        public void accumulate(Object val) 
        {
            for (Aggregate agg : aggregates) 
            {
                agg.accumulate(val);
            }
        }
 
        public Object result() 
        {
            Object[] arr = new Object[aggregates.length];
            for (int i = 0; i < aggregates.length; i++) 
            {
                arr[i] = aggregates[i].result();
            }
            return arr;
        }
 
        public void merge(Aggregate other) 
        {
            Aggregate[] otherAggregates = ((CompoundAggregate)other).aggregates;
            for (int i = 0; i < otherAggregates.length; i++) 
            {
                aggregates[i].merge(otherAggregates[i]);
            }
        }
 
        public CompoundAggregate(Aggregate... aggs) 
        {
            aggregates = aggs;
        }
 
        Aggregate[] aggregates;
    }