Sort treemap on value and return it as treemap agin.

Question

i have treemap and i sort it on value with code bellow. how can i get results as treemap again?

static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> entriesSortedByValues(
        Map<K, V> map) {
    SortedSet<Map.Entry<K, V>> sortedEntries = new TreeSet<Map.Entry<K, V>>(
            new Comparator<Map.Entry<K, V>>() {
                @Override
                public int compare(Map.Entry<K, V> e1, Map.Entry<K, V> e2) {
                    int res = e1.getValue().compareTo(e2.getValue());
                    return res != 0 ? res : 1;
                }
            });
    sortedEntries.addAll(map.entrySet());
    return sortedEntries;
}

Answer 1

You're creating a TreeSet, whereas, you need to create a TreeMap. The comparator which you pass to TreeMap, will use the map passed as parameter, to fetch the value and compare them.

Change your method to:

static <K, V extends Comparable<? super V>> TreeMap<K, V> entriesSortedByValues(final Map<K, V> map) {
    TreeMap<K, V> sortedEntries = new TreeMap<K, V>(new Comparator<K>() {
      @Override
      public int compare(K o1, K o2) {
        return map.get(o1).compareTo(map.get(o2));
      }
    });
    sortedEntries.putAll(map);
    return sortedEntries;
}

Tested with:

public static void main(String args[]) {
  Map<Integer, Integer> map = new HashMap<Integer, Integer>();
  map.put(1, 3);
  map.put(3, 1);
  map.put(5, 6);
  map.put(2, 10);
  // Prints: {3=1, 1=3, 5=6, 2=10}
  System.out.println(entriesSortedByValues(map));
}