为Java TreeSet创建比较器类

Question

我已经为Java的TreeSet函数创建了一个比较器类,我希望用它来命令消息.这个类看起来如下

public class MessageSentTimestampComparer
{
/// <summary>
/// IComparer implementation that compares the epoch SentTimestamp and MessageId
/// </summary>
/// <param name="x"></param>
/// <param name="y"></param>
/// <returns></returns>

public int compare(Message x, Message y)
{
    String sentTimestampx = x.getAttributes().get("SentTimestamp");
    String sentTimestampy = y.getAttributes().get("SentTimestamp");

    if((sentTimestampx == null) | (sentTimestampy == null))
    {
        throw new NullPointerException("Unable to compare Messages " +
                "because one of the messages did not have a SentTimestamp" +
                " Attribute");
    }

    Long epochx = Long.valueOf(sentTimestampx);
    Long epochy = Long.valueOf(sentTimestampy);

    int result = epochx.compareTo(epochy);

    if (result != 0)
    {
        return result;
    }
    else
    {
        // same SentTimestamp so use the messageId for comparison
        return x.getMessageId().compareTo(y.getMessageId());
    }
}
}

但是当我尝试使用这个类作为比较器时Eclipse给出了错误并告诉我删除了这个调用.我一直试图像这样使用这个类

private SortedSet<Message> _set = new TreeSet<Message>(new MessageSentTimestampComparer());

我还尝试将MessageSentTimestampComparer扩展为比较器但没有成功.有人可以解释我做错了什么.

Answer 1

你MessageSentTimestampComparer没有实施 Comparator.试试这个:

public class MessageSentTimestampComparer implements Comparator<Message> {
  @Override
  public int compare(Message x, Message y) {
    return 0;  // do your comparison
  }
}