list 求最大值，最小值，平均值等 已验证 可用

    public static void main(String[] args) {
        List list = new ArrayList();
        list.add(1);
        list.add(9);
        list.add(3);
        list.add(5);
        list.add(4);
        System.out.println(list);
        System.out.println("最大值: " + Collections.max(list));
        System.out.println("最小值: " + Collections.min(list));


        List lists = list;
        DoubleSummaryStatistics statistics =    lists.stream().mapToDouble(Number::doubleValue).summaryStatistics();

        System.out.println("最大值：" + statistics.getMax());
        System.out.println("最小值：" + statistics.getMin());
        System.out.println("平均值：" + statistics.getAverage());
        System.out.println("平均值四舍五入：" + Math.round(statistics.getAverage()));
        System.out.println("求和：" + statistics.getSum());
        System.out.println("计数：" + statistics.getCount());
    }