实现的比较逻辑的代码

	@Override
	public int compareTo(Message o) {
		// TODO Auto-generated method stub
		if (this.sequence == o.sequence) {
			return this.text.compareTo(o.text);
		}
		return Integer.compare(this.sequence, o.sequence);
	}

处理重复的代码
    static List<Message> process(List<Message> received) {
		// TODO: 按sequence去除重复消息
		Set<Message> set = new TreeSet<Message>(received);

		return List.copyOf(set);
	}