public static void main(String[] args) {
 User user1 = new User(1,"a","a");
 User user2 = new User(12,"b","b");
 User user3 = new User(5,"b","b");
 List<User> list = Arrays.asList(user1,user2,user3);
 list.forEach(System.out::println);
 // 排序,jdk1.8新方法,reversed表示倒序
 list.sort(Comparator.comparing(User::getId).reversed());

// List集合自带的排序方法
// list.sort(new Comparator<User>() {
// @Override
// public int compare(User o1, User o2) {
// return -o1.getId().compareTo(o2.getId());
// }
// });
 // Collections工具类中的排序方法
 Collections.sort(list, new Comparator<User>() {
 @Override
 public int compare(User o1, User o2) {
 return o1.getId().compareTo(o2.getId());
 }
 });
 list.forEach(System.out::println);
 }