//1.对int类型list进行求和
        Integer[] integerArray = {1, 3, 5, 10, 18};

        List<Integer> list = new ArrayList<>(Arrays.asList(integerArray));

        IntSummaryStatistics summaryStatistics = list.stream().mapToInt((s) -> s).summaryStatistics();
        System.out.println("总和：" + summaryStatistics.getSum());
        System.out.println("平均数：" + summaryStatistics.getAverage());
        System.out.println("总个数：" + summaryStatistics.getCount());
        System.out.println("最大值：" + summaryStatistics.getMax());
        System.out.println("最小值：" + summaryStatistics.getMin());

        //2.对list中的对象某个数值字段求和
        List<OrderReceivablesDetail> userList = new ArrayList<>();
        OrderReceivablesDetail user1 = new OrderReceivablesDetail();
        user1.setCollectionRatio(10.1);//double类型
        user1.setMoney(new BigDecimal(1000.1));//BigDecimal类型
        userList.add(user1);
        OrderReceivablesDetail user2 = new OrderReceivablesDetail();
        user2.setCollectionRatio(20.1);//double类型
        user2.setMoney(new BigDecimal(2000.1));//BigDecimal类型
        userList.add(user2);
        //写法1
        double collectionRatio = userList.stream().collect(Collectors.summingDouble(OrderReceivablesDetail::getCollectionRatio));
        System.out.println("比例总和 ：" + collectionRatio);
        //写法2
        double collectionRatio2 = userList.stream().mapToDouble(OrderReceivablesDetail::getCollectionRatio).sum();
        System.out.println("比例总和2： " + collectionRatio2);

        //3.对list中对象某个BigDecimal字段求和
        BigDecimal sumMoney = userList.stream().map(OrderReceivablesDetail::getMoney).reduce(BigDecimal.ZERO,BigDecimal::add);
        System.out.println("总金额： " + sumMoney);
       //说明：summingDouble方法是针对double类型的
        //summingLong  long类型
        //summingInt   Int类型

        //第二种转换法  方法
        //mapToLong  long类型
        //mapToDouble  double类型
        //mapToInt     Int类型