For example, let us consider I map a word and its corresponding counts in a particular document as shown below:

final Map<String, Integer> wordCounts = new HashMap<>();
wordCounts.put("USA", 100);
wordCounts.put("jobs", 200);
wordCounts.put("software", 50);
wordCounts.put("technology", 70);
wordCounts.put("opportunity", 200);

Now, if I have to sort this map with value in ascending order, then it would be simplest and readable as below:

final Map<String, Integer> sortedByCount = wordCounts.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));

Here, I am usingLinkedHashMap to store the sorted result to preserve the order of the elements in the resulting map.

The advantages of this approach are:

1. It doesn't modify the original data wordCounts, making it more thread safe.
2. It is more readable.

If you want to sort a map in reverse order, then you just need to specify comparing the value as reversed order as:

final Map<String, Integer> sortedByCount = wordCounts.entrySet()
                .stream()
                .sorted((Map.Entry.<String, Integer>comparingByValue().reversed()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));

The complete program for sorting in reverse order is:

public class SortMapByValueExample {
    public static Map<String, Integer> sortByValue(final Map<String, Integer> wordCounts) {

        return wordCounts.entrySet()
                .stream()
                .sorted((Map.Entry.<String, Integer>comparingByValue().reversed()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
    }

    public static void main(String[] args) {
        final Map<String, Integer> wordCounts = new HashMap<>();
        wordCounts.put("USA", 100);
        wordCounts.put("jobs", 200);
        wordCounts.put("software", 50);
        wordCounts.put("technology", 70);
        wordCounts.put("opportunity", 200);

        final Map<String, Integer> sortedByCount = sortByValue(wordCounts);

        System.out.println(sortedByCount);
    }
}

The output of the program is:

{jobs=200, opportunity=200, USA=100, technology=70, software=50}

You can see that the  sorted() method takesComparator as an argument, making it possible to sort a map with any kind of value. For example, the above sort can be written with the Comparator as:

public static Map<String, Integer> sortByValue(final Map<String, Integer> wordCounts) {

        return wordCounts.entrySet()
                .stream()
                .sorted((e1, e2) -> e2.getValue().compareTo(e1.getValue()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));
    }

You can implement Comparator with any kind of object. Isn't this a cool feature?

If you enjoyed this article and want to learn more about Java Collections, check out this collection of tutorials and articles on all things Java Collections.