How to sort a hash map using key descending order

Question

How to sort a hash map using key descending order. please explain with example. And how many way to sort a hash map. please explain in details

Answer 1

I suggest using this method as included in Java 8.

List<Map.Entry<String, Integer>> sorted_map =
                map_1.entrySet()
                .stream()
                .sorted(reverseOrder(Map.Entry.comparingByKey()))
                .collect(Collectors.toList());

Here 'map_1' is the map you want to sort.

Now you can use the sorted_map variable to iterate and use for your purpose.

Make sure to :

import static java.util.Collections.reverseOrder;

Answer 2

HashMaps don't support sorting. They store entries in buckets, how they see it fit, just based on the hashCode value of the keys. They are fine for storing things and looking them up afterwards, but unsuitable for iterating over their contents (which is what you apparently want to do) because you cannot rely on their order and iterating over it is usually expensive.

Try a TreeMap instead. You can specify a custom comparator that does just the reverse of the default comparator. In that case your entries will be ordered in descending order. Collections.reverseOrder will create such a comparator for you, you can use it like this:

new TreeMap<Integer, String>(Collections.reverseOrder());