jdk8 stream流

jdk8stream流的大致用法

下面展示一些 代码片。

 public static void main(String[] args) {

        ArrayList<User> list1 = new ArrayList<>();
        list1.add(new User(8,"张二狗"));
        list1.add(new User(10,"迪丽热巴"));
        list1.add(new User(3,"王麻子"));

        ArrayList<User> list2 = new ArrayList<>();

        list2.add(new User("洪七公"));
        list2.add(new User("杨幂"));
        list2.add(new User("尼古拉斯"));

        //集合转流，转集合
        List<User> users = list1.stream().filter((User user) -> user.getName().equals("迪丽热巴")).collect(Collectors.toList());
        //流
        java.util.stream.Stream<User> userStream = list1.stream().filter((User user) -> user.getAge() == 10);
        userStream.forEach(System.out :: println);

        //集合求最大值
        Optional<User> max = list1.stream().max((u1, u2) -> u1.getAge() - u2.getAge());
        User user = max.get();
        System.out.println(user);

        //求和
        list1.stream().map(User :: getAge).reduce(Integer::sum);

        //比较大小
        Optional<Integer> reduce = list1.stream().map(User::getAge).reduce(Integer::compareTo);
        Integer integer = reduce.get();
        System.out.println(integer);

        //分组
        Map<Integer, List<User>> collect = list1.stream().collect(Collectors.groupingBy(User::getAge))

    }