java8 按對象屬性值排序

//按id從小到大
List<User> sortUser = list.stream().sorted((u1, u2) -> u1.getId().compareTo(u2.getId())).collect(Collectors.toList());
////按id從大到小
List<User> sortUser = list.stream().sorted((u1, u2) -> u2.getId().compareTo(u1.getId())).collect(Collectors.toList());

示例：

public class HelloWorld {

    public static void main(String[] args) {
        List<User> list = new ArrayList<>();
        for(int i=1;i<=10;i++) {
            User u = new User(i, "用戶-" + i);
            list.add(u);
        }
        //按id從大到小排序
        List<User> sortUser = list.stream().sorted((u1, u2) -> u2.getId().compareTo(u1.getId())).collect(Collectors.toList());

        System.out.println("排序后：" + sortUser);
    }
    private static class User{
        Integer id;
        String name;

        public User(Integer id, String name) {
            this.id = id;
            this.name = name;
        }

        public Integer getId() {
            return id;
        }

        public void setId(Integer id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

}

執行結果：

[User {
    id = 10, name = '用戶-10'
}, User {
    id = 9, name = '用戶-9'
}, User {
    id = 8, name = '用戶-8'
}, User {
    id = 7, name = '用戶-7'
}, User {
    id = 6, name = '用戶-6'
}, User {
    id = 5, name = '用戶-5'
}, User {
    id = 4, name = '用戶-4'
}, User {
    id = 3, name = '用戶-3'
}, User {
    id = 2, name = '用戶-2'
}, User {
    id = 1, name = '用戶-1'
}]