TreeMap sort by value

Question

I want to write a comparator that will let me sort a TreeMap by value instead of the default natural ordering.

I tried something like this, but can\'t find out what

Answer 1

polygenelubricants answer is almost perfect. It has one important bug though. It will not handle map entries where the values are the same.

This code:...

Map nonSortedMap = new HashMap();
nonSortedMap.put("ape", 1);
nonSortedMap.put("pig", 3);
nonSortedMap.put("cow", 1);
nonSortedMap.put("frog", 2);

for (Entry entry  : entriesSortedByValues(nonSortedMap)) {
    System.out.println(entry.getKey()+":"+entry.getValue());
}

Would output:

ape:1
frog:2
pig:3

Note how our cow dissapeared as it shared the value "1" with our ape :O!

This modification of the code solves that issue:

static > SortedSet> entriesSortedByValues(Map map) {
        SortedSet> sortedEntries = new TreeSet>(
            new Comparator>() {
                @Override public int compare(Map.Entry e1, Map.Entry e2) {
                    int res = e1.getValue().compareTo(e2.getValue());
                    return res != 0 ? res : 1; // Special fix to preserve items with equal values
                }
            }
        );
        sortedEntries.addAll(map.entrySet());
        return sortedEntries;
    }