Question

I have a hashMap which has the following values as key value(sql date , integer) pairs:

a.put("31-05-2011",67);
a.put("01-06-2011",89);
a.put("10-06-2011",56);
a.put("25-05-2011",34);

when i try to sort the hashMap based on the keys using :
Map modified_a=new TreeMap(a);
and display the keys it is as follows :

01-06-2011,10-06-2011,25-05-2011, 31-05-2011

but I want the keys to be sorted as

31-05-2011,25-05-2011,01-06-2011 ,10-06-2011

I can see that the values are being sorted based on the first 2 digits( which is the date value) but I need the month value to also be considered and sort based on months first and then for each month sort the corresponding days.
Any clues ??

Answer 1

You can use like

Map<Date, Integer> m = new HashMap<Date, Integer>(); 

    DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy");

    m.put(new java.sql.Date(dateFormat.parse("31-05-2011").getTime()),67);
    m.put(new java.sql.Date(dateFormat.parse("01-06-2011").getTime()),89);
    m.put(new java.sql.Date(dateFormat.parse("10-06-2011").getTime()),56);
    m.put(new java.sql.Date(dateFormat.parse("25-05-2011").getTime()),34);


    Map<Date, Integer> m1 = new TreeMap(m);
    DateFormat df = new SimpleDateFormat("dd/MM/yyyy");

    for (Map.Entry<Date, Integer> entry : m1.entrySet())
    {
        System.out.println(df.format(entry.getKey()));
    }