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- Sorting hashmap based on keys 8 answers
I trying to sort this HashMap based on date in keys
My Hash map:
Map<Date, ArrayList> m = new HashMap<Date, ArrayList>();
Use a TreeMap
instead of HashMap
. As Date
already implements Comparable
, it will be sorted automatically on insertion.
Map<Date, ArrayList> m = new TreeMap<Date, ArrayList>();
Alternatively, if you have an existing HashMap
and want to create a TreeMap
based on it, pass it to the constructor:
Map<Date, ArrayList> sortedMap = new TreeMap<Date, ArrayList>(m);
See also:
Use TreeMap instead of HashMap to store the data,it will be sorted automatically.
来源:https://stackoverflow.com/questions/8298290/how-to-sort-hashmap-based-on-date