How to sort a Java HashMap by value

A HashMap can be sorted by its keys or its values. However, a problem that HashMap has is that its iteration order, when considering a sorted data structure, is not preserved. This makes it difficult to display sorted data.

One solution to this problem is to use the LinkedHashMap class in Java; this class maintains the iteration order. In fact, any other class will work as well, provided that it keeps the iteration order the same.

Since a LinkedHashMap keeps key-value pairs in the insertion order, the following will be our procedure to get a sorted LinkedHashMap:

Sorting a HashMap by value

1. Extract the HashMap’s entries (using HashMap.entrySet()) and input them into an ArrayList (has elements of type Map.Entry<String, Integer>) with a simple for-each loop:

for(Map.Entry<String, Integer> e: hashMap.entrySet()) {
			arr.add(e);
}

2. Sort this ArrayList using Collections.sort(). As the elements of this ArrayList are of type Map.Entry<String, Integer>, we need to write our own Comparator code to sort the elements:

Comparator<Map.Entry<String, Integer>> myComparator =
new Comparator<Map.Entry<String, Integer>>() {
            
            @Override
            public int compare(
                  Map.Entry<String, Integer> e1,
                  Map.Entry<String, Integer> e2) {

                Integer int1 = e1.getValue();
                Integer int2 = e2.getValue();
                return int1.compareTo(int2);
            }
};

// Sorting the list w.r.t values of entries using myComparator
Collections.sort(list, myComparator);

3. Add all the elements (or entries) of the sorted ArrayList to a LinkedHashMap:

for(Map.Entry<String, Integer> e: list) {
			linkedMap.put(e.getKey(), e.getValue());
}

4. Finally, we can print our LinkedHashMap; the data will be sorted:

for(Map.Entry<String, Integer> e: linkedMap) {
			System.out.println(e.getValue());
}

Example code