How Can I Sort a Java HashMap by Its Values?

Sorting a HashMap in Java: Value-Based Techniques

In Java, HashMaps are valuable collections for storing key-value pairs, but they do not maintain a specific sorting order. To sort a HashMap based on values, we need to employ additional techniques.

Approaches for Value-Based Sorting

One approach is to convert the HashMap to a list of values using the values() method. We can then sort the list using a comparator that defines the desired sorting logic.

Map<String, Person> people = new HashMap<>();
Person jim = new Person("Jim", 25);
Person scott = new Person("Scott", 28);
Person anna = new Person("Anna", 23);

people.put(jim.getName(), jim);
people.put(scott.getName(), scott);
people.put(anna.getName(), anna);

List<Person> peopleByAge = new ArrayList<>(people.values());
Collections.sort(peopleByAge, Comparator.comparing(Person::getAge));

After sorting the list, we can access the sorted elements.

Another approach, suitable for frequent access, is to create a HashMap mapping to a sorted set. For instance, we could use a HashMap> to achieve this.

Consideration for TreeMap

If sorting by key is preferred, it's worth considering using a TreeMap instead. TreeMaps automatically maintain a natural sorting order based on the keys.

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