How to iterate hashmap in reverse order in Java

Map<Integer, List<String>> sortedMap = new TreeMap<Integer, List<String>>(Collections.reverseOrder());

Collections.reverseOrder() keeps the map sorted in descending order.

A HashMap doesn't maintain eny order between keys.

A TreeMap orders its keys by their natural order, or by the order imposed by a comparator that you pass when constructing the map. So if you want to have Integer keys ordered in reverse order, construct the TreeMap this way:

Map<Integer, List<String>> sortedMap = 
    new TreeMap<Integer, List<String>>(Collections.reverseOrder());

Hashmap does not have specific order. But you can use TreeMap.

Perhaps this simple example can help you :

Map<Integer, String> map = new TreeMap<Integer, String>();
        map.put(1, "abc1");
        map.put(2, "abc2");
        map.put(3, "abc3");

        ArrayList<Integer> keys = new ArrayList<Integer>(map.keySet());
        for(int i=keys.size()-1; i>=0;i--){
            System.out.println(map.get(keys.get(i)));
        }

best approach to acheive iteration of hashmap in reverse order

HashMap does not define any particular ordering of its element. Therefore the "reverse" order isn't defined either.

For a TreeMap, you can use descendingMap().