How to Sort a Java HashMap by Values in Ascending and Descending Order?

Sorting a HashMap by Values

In Java, the HashMap data structure provides a convenient way to store key-value pairs. However, if you need to access the data based on the values associated with the keys, sorting the HashMap by values is necessary.

Sorting a HashMap in Ascending Order

One approach to sorting a HashMap by values is to use a Java 8 stream. The following code snippet demonstrates how to do this in ascending order:

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class SortHashMapByValues {

    public static void main(String[] args) {
        // Create an unsorted HashMap
        HashMap<Integer, String> unsortedMap = new HashMap<>();
        unsortedMap.put(1, "froyo");
        unsortedMap.put(2, "abby");
        unsortedMap.put(3, "denver");
        unsortedMap.put(4, "frost");
        unsortedMap.put(5, "daisy");

        // Sort the HashMap by values in ascending order
        Map<Integer, String> sortedMapAsc = unsortedMap.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue())
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));

        // Key, Value : 2, abby
        // Key, Value : 5, daisy
        // Key, Value : 3, denver
        // Key, Value : 4, frost
        // Key, Value : 1, froyo
        System.out.println(sortedMapAsc);
    }
}

Sorting a HashMap in Descending Order

To sort a HashMap by values in descending order, slightly modify the code snippet above:

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class SortHashMapByValues {

    public static void main(String[] args) {
        // Create an unsorted HashMap
        HashMap<Integer, String> unsortedMap = new HashMap<>();
        unsortedMap.put(1, "froyo");
        unsortedMap.put(2, "abby");
        unsortedMap.put(3, "denver");
        unsortedMap.put(4, "frost");
        unsortedMap.put(5, "daisy");

        // Sort the HashMap by values in descending order
        Map<Integer, String> sortedMapDesc = unsortedMap.entrySet()
                .stream()
                .sorted(Map.Entry.<Integer, String>comparingByValue().reversed())
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));

        // Key, Value : 1, froyo
        // Key, Value : 4, frost
        // Key, Value : 3, denver
        // Key, Value : 5, daisy
        // Key, Value : 2, abby
        System.out.println(sortedMapDesc);
    }
}

This code will output the sorted HashMap with keys representing the original keys and values sorted in descending order. Both the ascending and descending order examples use a LinkedHashMap to maintain insertion order, ensuring that the keys are properly associated with the sorted values.

The above is the detailed content of How to Sort a Java HashMap by Values in Ascending and Descending Order?. For more information, please follow other related articles on the PHP Chinese website!