Question

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How to sort a Map<Key, Value> on the values in Java?

I have a treemap<Integer,Float>. How can I sort the the map on float point number?

Is there any quick way? or I have to write the comparator for the map?

Answer 1

In practice, you can’t (correctly, reliably) sort a Map implementation by the values. (The implementations you might see claiming otherwise are hackish, unreliable, and behave really weirdly — rejecting duplicate values, throwing exceptions on attempts to look at keys not in the map, getting unrecoverably corrupted if the backing map changes…)

Instead, sort the list of entries explicitly:

List<Map.Entry<Integer, Float>> list = new ArrayList<>(map.entrySet());
Collections.sort(list, new Comparator<Map.Entry<Integer, Float>>() {
  public int compare(Map.Entry<Integer, Float> e1, Map.Entry<Integer, Float> e2){
    return e1.getValue().compareTo(e2.getValue());
  }
});

If you liked, you could then put this into a LinkedHashMap:

Map<Integer, Float> sortedMap = new LinkedHashMap<Integer, Float>();
for (Map.Entry<Integer, Float> entry : list) {
  sortedMap.put(entry.getKey(), entry.getValue());
}