List＜Integer＞ 快速求和 平均值等
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<Integer> 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());
}
