How to sort TreeMap by value not by Key

Question

Possible Duplicate:
TreeMap sort by value

Hi I want to sort TreeMap Collection by value not by its key. For eg,

 TreeMap map=new TreeMap();
    map.put(new Integer(100),"ccc");
    map.put(new Integer(300),"bbb");
    map.put(new Integer(200),"ddd");
    map.put(new Integer(400),"aaa");

It should be ordered as,

1) 400 -> aaa
2) 300 -> bbb
3) 100 -> ccc
4) 200 -> ddd

http://stackoverflow.com/questions/2864840/treemap-sort-by-value — squiguy, Dec 19 '12 at 01:42
what is the issue in using those values as keys? why do you want to force them as values — vishal_aim, Dec 19 '12 at 04:08

score 1 · Accepted Answer · answered Dec 19 '12 at 05:02

You need a special iterator, try this

...
    Iterator i = valueIterator(map);
    while(i.hasNext()) {
        System.out.println(i.next());
    }
...
    Iterator valueIterator(TreeMap map) {
        Set set = new TreeSet(new Comparator<Map.Entry<Integer, String>>() {
            @Override
            public int compare(Entry<Integer, String> o1, Entry<Integer, String> o2) {
                return  o1.getValue().compareTo(o2.getValue()) > 0 ? 1 : -1;
            }
        });
        set.addAll(map.entrySet());
        return set.iterator();
    }

output

400=aaa
300=bbb
100=ccc
200=ddd

You can extend TreeMap and add this method to it. Note that the Comparator allows duplicate values because it never returns 0.

How to sort TreeMap by value not by Key

1 Answers1