Question

我有一个名为channelsList的频道列表。

List<Channel> channelsList;

频道类

public class Channel{
    public Conversation conversation;
}

会话班

public class Conversation{
    public String sentAt;
}

我需要按照myDate的降序对频道列表进行排序。我怎样才能使用比较器呢？到目前为止我试过这个。但这不起作用，因为我的收集频道可以具有会话的空值，并且会话可以具有sentAt的空值。任何帮助将不胜感激。

 Collections.sort(channelsList, new Comparator<Channel>() {
        DateFormat format = new SimpleDateFormat(DATE_FORMAT_PATTERN);

        @Override
        public int compare(Channel o1, Channel o2) {
            try {
                if (o1.getConversation() != null && Util.isUTCFormat(o1.getConversation().getSentAt()) && o2.getConversation() != null && Util.isUTCFormat(o2.getConversation().getSentAt()))
                    return format.parse(o1.getConversation().getSentAt()).compareTo(format.parse(o2.getConversation().getSentAt()));
                else
                    return -1;

            } catch (ParseException e) {
                throw new IllegalArgumentException(e);
            }              
        }
    });

Answer 1

Collections.sort(channelsList, new Comparator<Channel>() {
    DateFormat format = new SimpleDateFormat(DATE_FORMAT_PATTERN);

    @Override
    public int compare(Channel o1, Channel o2) {
        // If both are null, they are equal
        if (o1.getConversation() == null && o2.getConversation() == null)
            return 0;

        // If only first one is null, it is less than the other (null's come first)
        if (o1.getConversation() == null)
            return -1;

        // If only second one is null, it is greater than the other
        if (o2.getConversation() == null)
            return 1;

        Conversation c1 = o1.getConversation();
        Conversation c2 = o2.getConversation();

        // Same comparisons are done here again
        if (c1.getSentAt() == null && c2.getSentAt() == null)
            return 0;

        if (c1.getSentAt() == null)
            return -1;

        if (c2.getSentAt() == null)
            return 1;

        try {
            if (Util.isUTCFormat(o1.getConversation().getSentAt()) && Util.isUTCFormat(o2.getConversation().getSentAt()))
                return format.parse(o1.getConversation().getSentAt()).compareTo(format.parse(o2.getConversation().getSentAt()));
            else
                return -1;

        } catch (ParseException e) {
            throw new IllegalArgumentException(e);
        }              
    }
});

Answer 2

您可以使用比较器或类似物来对数组进行排序

Java字符串日期比较器

2 个答案: