list.stream().mapToDouble(User::getHeight).sum()//和 list.stream().mapToDouble(User::getHeight).max()//最大 list.stream().mapToDouble(User::getHeight).min()//最小 list.stream().mapToDouble(User::getHeight).average()//平均值
二:stream分组
List<User> collect = Stream.of(User.builder().id(1L).name("张三").build(), User.builder().id(1L).name("李四").build(), User.builder().id(2L).name("王二").build()).collect(Collectors.toList()); Map<Long, List<User>> collect1 = collect.stream().collect(Collectors.groupingBy(User::getId)); collect1.forEach((k,v)->{ System.out.println(k); });