list去重排序

实体对象
public class User {
    private int id;
    private String username;
    private String password;
    private Date createTime;
    public User(int id, String username, String password, Date createTime) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.createTime = createTime;
    }
}
user集合
List<User> list = new ArrayList<User>();
list.add(new User(4, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:11")));
list.add(new User(3, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:12")));
list.add(new User(2, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:13")));
list.add(new User(1, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:11")));
list.add(new User(1, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:11")));
list.add(new User(1, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:11")));
list.add(new User(1, "a", "aa",new SimpleDateFormat("yyyy-MM-dd HH:mm-ss").parse("2018-08-15 11:11:14")));

去重排序方法（按照id,id必须是整型）
private static List<User> removeDuplicateUser(List<User> users) {
    Set<User> set = new TreeSet<User>(new Comparator<User>() {
        @Override
        public int compare(User o1, User o2) {
            return (int)(o1.getId() - (o2.getId()));
        }
    });
    set.addAll(users);
    return new ArrayList<User>(set);
}
执行结果：
User{id=1, username='a', password='aa', createTime='Wed Aug 15 11:11:14 CST 2018'}
User{id=2, username='a', password='aa', createTime='Wed Aug 15 11:11:13 CST 2018'}
User{id=3, username='a', password='aa', createTime='Wed Aug 15 11:11:12 CST 2018'}
User{id=4, username='a', password='aa', createTime='Mon Aug 13 11:11:11 CST 2018'}
去重排序方法（按照id,id必须是整型）
private static List<User> removeDuplicateUserByTime(List<User> users) {

    Set<User> set = new TreeSet<User>(new Comparator<User>() {
        @Override
        public int compare(User o1, User o2) {
            return (o1.getCreateTime().compareTo((o2.getCreateTime())));
        }
    });
    set.addAll(users);
    return new ArrayList<User>(set);
}执行结果
User{id=4, username='a', password='aa', createTime='Wed Aug 15 11:11:11 CST 2018'}
User{id=3, username='a', password='aa', createTime='Wed Aug 15 11:11:12 CST 2018'}
User{id=2, username='a', password='aa', createTime='Wed Aug 15 11:11:13 CST 2018'}
User{id=1, username='a', password='aa', createTime='Wed Aug 15 11:11:14 CST 2018'}