Sorting Descending order: Java Map

Question

What I want to do is sort a map by value. I went over many questions that are available on the stackoverflow site and found out following solution that does what I want but missing a small thing.

Link1: Sorting Map

But the issue I am running into is that by default this is sorted by ascending order by value. I want to order it by descending order:

So what I did was I created a class that implements a comparator

class MyComparator implements Comparator {     Map map;     public MyComparator(Map map) {         this.map = map;     }     public int compare(Object o1, Object o2) {         return ((Integer) map.get(o2)).compareTo((Integer) map.get(o1));     } } 

And then I pass my map to the treemap,

MyComparator comp = new MyComparator(myMap); Map<String, Integer> newMap = new TreeMap(comp); newMap.putAll(myMap); 

This seems like bad approach because I feel this is inefficient. Is there a way to change the solution in the link to do ordering on descending order by default.

Answer 1

You should use new TreeMap<>(Collections.reverseOrder());.

Map<String, Integer> newMap = new TreeMap<>(Collections.reverseOrder()); newMap.putAll(myMap); 

or to reverse an existing comparator like the value-comparator Collections.reverseOrder(comparator). It works like your approach swapping the two objects before invoking compare/compareTo.

Answer 2

    TreeMap<Long,String> treeMap = new TreeMap<Long,String>();      NavigableMap <Long, String> nmap = treeMap.descendingMap();      Set<Long, String> set = nmap.entrySet();      Iterator<Long, String> iterator = set.iterator(); 

now u can iterate over iterator and extract the value using iterator.hasNext() and iterator.next() methods ......