java中stream流的用法

程序猿_Jerry

已于 2023-03-29 15:01:07 修改

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文章标签： java jvm 开发语言

于 2022-09-15 09:38:53 首次发布

本文链接：https://blog.youkuaiyun.com/weixin_48524022/article/details/126864939

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1.将集合转为map
Map<Integer, Integer> map= list.stream().collect(Collectors.toMap(k1 -> k1.getReason(), k2 -> k2.getTotal()));

2.讲集合中的对象根据某个字段分组

        taskGroupDtos.stream().collect(Collectors.groupingBy(TaskGroupDto :: getType,Collectors.mapping(value -> value,Collectors.toList())));

3.排序

 List<User> personList = new ArrayList<>();
        personList.add(new User("张三", 16, 181));
        personList.add(new User("李四", 17, 180));
        personList.add(new User("王五", 16, 179));
        personList.add(new User("张明", 18, 177));
        personList.add(new User("李威", 16, 190));
        personList.add(new User("王鹏", 15, 188));
        personList.add(new User("王莉", 17, 177));
 
        //年龄升序，相同年龄身高升序
        List<User> ascPList = personList.stream()
                .sorted(Comparator.comparingInt(User::getAge).thenComparing(User::getHeight))
                .collect(Collectors.toList());
        //年龄降序，相同年龄身高降序
        List<User> descPList = personList.stream()
                .sorted(Comparator.comparingInt(User::getAge).thenComparing(User::getHeight).reversed())
                .collect(Collectors.toList());