How to sort HashMap based on Date? [duplicate]

问题

This question already has an answer here:

• 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>();

回答1:

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:

• Java tutorials - Map implementations
• Java tutorials - Object ordering

回答2:

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