import java.util.*;public class Test1 {    public static void main(String[] args) {        List<Message> received = Arrays.asList(                new Message(1, "Hello!"),                new Message(2, "发工资了吗？"),                new Message(2, "发工资了吗？"),                new Message(3, "去哪吃饭？"),                new Message(3, "去哪吃饭？"),                new Message(4, "Bye")        );        List<Message> displayMessages = process(received);        for (Message message : displayMessages) {            System.out.println(message.text);        }    }    static List<Message> process(List<Message> received) {        // TODO: 按sequence去除重复消息        Set<Message> s = new TreeSet<>((m1, m2) -> {            if (m1.sequence == m2.sequence) return 0;            return m1.sequence > m2.sequence ? 1 : -1;        });        s.addAll(received);        received = new ArrayList<Message>(s);        return received;    }}class Message {    public final int sequence;    public final String text;    public Message(int sequence, String text) {        this.sequence = sequence;        this.text = text;    }}