See http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html.
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.
Question
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();
}
}
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 ?
Solution
See http://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html.
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.
OTHER TIPS
It looks like the lines
data = line.split(":"); map.put(df.parse(data[1]), line);
Are effectively parsing out only the month. Line.split(":") is going to produce an array split by : . If you have dates formatted in your data file dd:mm:yyyy then the resulting array "data" should be {[dd], [mm], [yyyy]}. So data[1] is going to simply be the month.
I could be wrong, but I suspect this is why you are only getting the 12 key-value pairs; you are parsing only for the month, and any time you get a new month key, you're overwriting the old key.