A TreeMap is always sorted based on its keys, however if you want to sort it based on its values then you can build a logic to do this using comparator. Below is a complete code of sorting a TreeMap by values.
import java.util.*; class TreeMapDemo { //Method for sorting the TreeMap based on values public static <K, V extends Comparable<V>> Map<K, V> sortByValues(final Map<K, V> map) { Comparator<K> valueComparator = new Comparator<K>() { public int compare(K k1, K k2) { int compare = map.get(k1).compareTo(map.get(k2)); if (compare == 0) return 1; else return compare; } }; Map<K, V> sortedByValues = new TreeMap<K, V>(valueComparator); sortedByValues.putAll(map); return sortedByValues; } public static void main(String args[]) { TreeMap<String, String> treemap = new TreeMap<String, String>(); // Put elements to the map treemap.put("Key1", "Jack"); treemap.put("Key2", "Rick"); treemap.put("Key3", "Kate"); treemap.put("Key4", "Tom"); treemap.put("Key5", "Steve"); // Calling the method sortByvalues Map sortedMap = sortByValues(treemap); // Get a set of the entries on the sorted map Set set = sortedMap.entrySet(); // Get an iterator Iterator i = set.iterator(); // Display elements while(i.hasNext()) { Map.Entry me = (Map.Entry)i.next(); System.out.print(me.getKey() + ": "); System.out.println(me.getValue()); } } }
Output:
Key1: Jack Key3: Kate Key2: Rick Key5: Steve Key4: Tom
Khushboo Agrawal says
Hi,
Here in the above example, after sorting the keys with comparator, you have put the values back in a new Tree HashMap , which will by default sort if by keys.
You should have put them in a LinkedHashMap instead.
amishra says
is this java8?