Sorting the Map<Key,Value> in descending order based on the value [duplicate]

Question

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

I am using map interface to read from a file and then store the values in that as a key value pair. The file format is as follows

 A 34  B 25  c 50 

I will read the datas from this file and store that as a key value pair and then I will display this to the user. My requirement is to display the results in this format

C 50 A 34 B 25 

Thus I need to sort the map in descending order of the value. So that I will be able to display these as my result .. I have read about this and find the below code

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; // Special fix to preserve items with equal values                 }             }         );         sortedEntries.addAll(map.entrySet());         return sortedEntries;     } 

I hope this is gonna sort the values in ascending order, I just want to know whether this approach is correct or some other effective approach will be helpful for me ?

Answer 1

Since you can have duplicate values you shouldn't be using a Set at all. Change to a List and sort it instead. Your entriesSortedByValues would look something like this:

static <K,V extends Comparable<? super V>>              List<Entry<K, V>> entriesSortedByValues(Map<K,V> map) {      List<Entry<K,V>> sortedEntries = new ArrayList<Entry<K,V>>(map.entrySet());      Collections.sort(sortedEntries,              new Comparator<Entry<K,V>>() {                 @Override                 public int compare(Entry<K,V> e1, Entry<K,V> e2) {                     return e2.getValue().compareTo(e1.getValue());                 }             }     );      return sortedEntries; } 

Note: in your example output the values is descending. If you want them ascending, use e1.getValue().compareTo(e2.getValue()) instead.

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Example:

public static void main(String args[]) {      Map<String, Integer> map = new HashMap<String, Integer>();     map.put("A", 34);     map.put("B", 25);     map.put("C", 50);     map.put("D", 50); // "duplicate" value      System.out.println(entriesSortedByValues(map)); } 

Output:

[D=50, C=50, A=34, B=25]