RealSum与IntegerSum

RealSumAggregate 实现了对实数（以双精度值形式）的求和聚合，而 IntegerSumAggregate 实现了对整数（以长整型形式）的求和聚合。

类定义

RealSumAggregate

用于实数值的求和：

    public static class RealSumAggregate implements Aggregate<Number>
    {
        public void initialize(Number val) 
        {
            sum = val.doubleValue();
        }
 
        public void accumulate(Number val) 
        {
            sum += val.doubleValue();
        }
 
        public Object result() 
        {
            return new Double(sum);
        }
         
        public void merge(Aggregate<Number> other) 
        {
            sum += ((RealSumAggregate)other).sum;
        }
 
        double sum;
    }

IntegerSumAggregate

用于整数值的求和聚合：

    public static class IntegerSumAggregate implements Aggregate<Number>
    {
        public void initialize(Number val) 
        {
            sum = val.longValue();
        }
 
        public void accumulate(Number val) 
        {
            sum += val.longValue();
        }
         
        public Object result() 
        {
            return new Long(sum);
        }
 
        public void merge(Aggregate<Number> other) 
        {
            sum += ((IntegerSumAggregate)other).sum;
        }
 
        long sum;
    }