按日期键在Java中排序地图 [英] Sorting a map by date key in Java

问题描述

我正在使用TreeMap按日期键在java中排序地图。这是我的代码

I'm trying to sort a map in java by date key using TreeMap. Here's my code

public static void sort() {

    BufferedReader br;
    String line;
    String[] data;
    Date date ;
    DateFormat df = new SimpleDateFormat("dd-mm-YYY");

    Map<Date,String> map = new TreeMap<Date,String>();

    try {
        br = new BufferedReader(new FileReader(
                "/home/user/Desktop/train/2013-training_set.txt"));

        int i=0;
        while ((line = br.readLine()) != null) {
            ++i;
            data = line.split(":");
            map.put(df.parse(data[1]), line);
        }

        System.out.println(map.size()+" i = "+i);

        Set st = mp.entrySet();
        Iterator it = st.iterator();

        while (it.hasNext()) {

            Map.Entry me = (Map.Entry) it.next();
            System.out.print(me.getKey() + "->:");
            System.out.println(me.getValue());
        }

    } catch (Exception e) {
        e.printStackTrace();
    }
}

date [1] 包含字符串格式的日期，如（21-3-2013）。问题是它存储在TreeMap（mp）中只有12个键值对（每个月一个），而不是103（i）预期。任何想法？

The date[1] contains the date in string format and looks like (e.g. 21-3-2013). The problem is that it stores in the TreeMap(mp) only 12 key-value pairs(one for each month) instead of the 103(i) expected. Any ideas ?

推荐答案

请参阅 http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html 。

年份中使用y，年份中为M，月中为d。具体来说，小写字母m以小时为单位，而大写字母M为年份的月份。

Use y for year, M for month in year, and d for day in month. Specifically, lowercase m is minute in hour, while uppercase M is month in year.

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