Best efficient way to sort Months and Year in Java

Question

I have a list which contains dates in format (MON-YYYY) in string format, I need to sort this list.The approach I have followed till now is reading the list and converting the string in date format and using compare option, but i am not getting the desired result

Code Snippet

List<String> abc = new ArrayList<String>();
        List<Date> xyz = new ArrayList<Date>();

        abc.add("JAN-2010");
        abc.add("JAN-2011");
        abc.add("APR-2013");
        abc.add("NOV-2009");

        try {

            for (String abc1 : abc) {

                Date date;

                date = new SimpleDateFormat("MMM-yyyy", Locale.ENGLISH)
                        .parse(abc1);
                xyz.add(date);

            }

            Collections.sort(xyz, new Comparator<Date>() {

                public int compare(Date arg0, Date arg1) {
                    // return arg0.getDate().compareTo(o2.getDate());
                    return arg0.compareTo(arg1);
                }
            });

            for (Date date1 : xyz) {
                System.out.println("Sorted : " + date1);
            }

        } catch (ParseException e) {

            e.printStackTrace();

        }
    }

Output

    Sorted : Sun Nov 01 00:00:00 IST 2009
Sorted : Fri Jan 01 00:00:00 IST 2010
Sorted : Sat Jan 01 00:00:00 IST 2011
Sorted : Mon Apr 01 00:00:00 IST 2013

Expected Output

NOV-2009
JAN-2010
JAN-2011
APR-2013

I am also not sure if the above code is perfect in performance perspective as converting the string and parsing would take a long time if I have thousands of dates in MON-YYYY format in the list.

Answer 1

Ok, I see you corrected the typo.

Now, remember you need to use a DateFormatter also when you present the data, in addition to when you parse it.

So please try this:

        for (Date date1 : xyz) {
            System.out.println("Sorted : " + new SimpleDateFormat("MMM-yyyy", Locale.ENGLISH).format(date1));
        }

You might want to make the SimpleDateFormat available to all methods of your class as a field.

Additional info: please be aware SimpleDateFormat is known to not be thread-safe. You can use ThreadLocal as one solution to that.

Good luck.

Answer 2

You've parsed your dateString to actual Date object. And java.util.Date can't be formatted. Only a String representation of that Date object can be got.

You need to change your comparator to compare your dateString format by internally converting the Strings to date.

If you are gonna sort the Date objects, you'll get the output you've got. Also, as mentioned by @darijan , change your logic in the comparator.

Answer 3

First i think it's better to have only one instance of SimpleDateFormat and always use this to parse your dates.
I also suggest to create this instance of SimpleDateFormat in front of your try block, so you solve your second problem and can use SimpleDateFormat.format(date) to parse your dates back to requested stringformat.