java - How to sort map by calendar in string type? -

i have structure:

map<string, string> map = new hashmap<string, string>(); 

and data looks this:

("10/11/2015", "a") ("10/12/2015", "b") ("10/13/2015", "c") ("10/14/2015", "d") ("10/15/2015", "e") 

i want sort map date (key), attempt convert string calendar type , move them treemap below:

dateformat formatter = new simpledateformat("mm/dd/yyyy"); calendar calendar = calendar.getinstance();  treemap<calendar, string> tree = new treemap<calendar, string>();  for(map.entry<string, string> entry : map.entryset()){     string key = entry.getkey();     string value =  entry.getvalue();      calendar.settime(formatter.parse(key));     tree.put(calendar, value); } 

but when print key, result looks below:

10/11/2015 10/15/2015 10/14/2015 10/12/2015 10/13/2015 

what should sort map date (date in string type) correctly?

based on example, should end treemap single calendar key, because you're using same instance of calendar.

instead, if used new instance of calendar each entry, example...

    dateformat formatter = new simpledateformat("mm/dd/yyyy");      map<string, string> map = new hashmap<>();     map.put("10/11/2015", "a");     map.put("10/12/2015", "b");     map.put("10/13/2015", "c");     map.put("10/14/2015", "d");     map.put("10/15/2015", "e");      treemap<calendar, string> tree = new treemap<calendar, string>();      (map.entry<string, string> entry : map.entryset()) {         system.out.println(entry);         string key = entry.getkey();         string value = entry.getvalue();          calendar calendar = calendar.getinstance();         calendar.settime(formatter.parse(key));         tree.put(calendar, value);     }      (calendar key : tree.keyset()) {         system.out.println(key.gettime());     } 

it print more like...

sun oct 11 00:00:00 est 2015 mon oct 12 00:00:00 est 2015 tue oct 13 00:00:00 est 2015 wed oct 14 00:00:00 est 2015 thu oct 15 00:00:00 est 2015 

if you're using java 8(+), should using new date/time api, example...

map<localdate, string> tree = new treemap<>();  (map.entry<string, string> entry : map.entryset()) {     system.out.println(entry);     string key = entry.getkey();     string value = entry.getvalue();      localdate ld = localdate.parse(key, datetimeformatter.ofpattern("mm/dd/yyyy"));     tree.put(ld, value); }  (localdate key : tree.keyset()) {     system.out.println(key); }