How to Sort a Map by Values in Java - Step by Step Examples

How to Sort a Map by Values in Java ?

Answer

To sort a map by values in Java, you can convert the map entries to a list, sort the list by values, and then convert it back to a map. This method allows you to sort the map based on values.

✐ Examples

1 Sorting a Map by Values Using List Conversion

We can sort a map by values in Java by converting the map entries to a list, sorting the list by values, and then converting it back to a map.

For example,

We start by importing the java.util.HashMap, java.util.LinkedHashMap, java.util.List, java.util.Map, and java.util.stream.Collectors classes, which provide the necessary functions and data structures for working with maps and lists.
We declare and initialize a `HashMap` named unsortedMap with some key-value pairs. In this example, the map has string keys and integer values.
We convert the map entries to a list and sort the list by values using streams.
We create a new `LinkedHashMap` from the sorted list of map entries to maintain the insertion order.
We print the sorted map to the console using the `System.out.println` function to verify the sorting.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize an unsorted map
        Map<String, Integer> unsortedMap = new HashMap<>();
        unsortedMap.put("apple", 3);
        unsortedMap.put("banana", 1);
        unsortedMap.put("cherry", 2);

        // Convert the map entries to a list and sort the list by values
        List<Map.Entry<String, Integer>> sortedEntries = unsortedMap.entrySet()
            .stream()
            .sorted(Map.Entry.comparingByValue())
            .collect(Collectors.toList());

        // Create a new map from the sorted list of map entries
        Map<String, Integer> sortedMap = new LinkedHashMap<>();
        for (Map.Entry<String, Integer> entry : sortedEntries) {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        // Print the sorted map
        System.out.println("Sorted Map by Values: " + sortedMap);
    }
}

Output

Sorted Map by Values: {banana=1, cherry=2, apple=3}

2 Sorting a Map by Values in Descending Order

We can sort a map by values in descending order in Java by converting the map entries to a list, sorting the list by values in descending order, and then converting it back to a map.

For example,

We start by importing the java.util.HashMap, java.util.LinkedHashMap, java.util.List, java.util.Map, and java.util.stream.Collectors classes, which provide the necessary functions and data structures for working with maps and lists.
We declare and initialize a `HashMap` named unsortedMap with some key-value pairs. In this example, the map has string keys and integer values.
We convert the map entries to a list and sort the list by values in descending order using streams.
We create a new `LinkedHashMap` from the sorted list of map entries to maintain the insertion order.
We print the sorted map to the console using the `System.out.println` function to verify the sorting.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize an unsorted map
        Map<String, Integer> unsortedMap = new HashMap<>();
        unsortedMap.put("apple", 3);
        unsortedMap.put("banana", 1);
        unsortedMap.put("cherry", 2);

        // Convert the map entries to a list and sort the list by values in descending order
        List<Map.Entry<String, Integer>> sortedEntries = unsortedMap.entrySet()
            .stream()
            .sorted(Map.Entry.<String, Integer>comparingByValue().reversed())
            .collect(Collectors.toList());

        // Create a new map from the sorted list of map entries
        Map<String, Integer> sortedMap = new LinkedHashMap<>();
        for (Map.Entry<String, Integer> entry : sortedEntries) {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        // Print the sorted map
        System.out.println("Sorted Map by Values (Descending): " + sortedMap);
    }
}

Output

Sorted Map by Values (Descending): {apple=3, cherry=2, banana=1}

3 Sorting a Map with Numeric Keys by Values

We can sort a map with numeric keys by values in Java by converting the map entries to a list, sorting the list by values, and then converting it back to a map.

For example,

We start by importing the java.util.HashMap, java.util.LinkedHashMap, java.util.List, java.util.Map, and java.util.stream.Collectors classes, which provide the necessary functions and data structures for working with maps and lists.
We declare and initialize a `HashMap` named unsortedMap with some key-value pairs. In this example, the map has integer keys and string values.
We convert the map entries to a list and sort the list by values using streams.
We create a new `LinkedHashMap` from the sorted list of map entries to maintain the insertion order.
We print the sorted map to the console using the `System.out.println` function to verify the sorting.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare and initialize an unsorted map
        Map<Integer, String> unsortedMap = new HashMap<>();
        unsortedMap.put(3, "three");
        unsortedMap.put(1, "one");
        unsortedMap.put(2, "two");

        // Convert the map entries to a list and sort the list by values
        List<Map.Entry<Integer, String>> sortedEntries = unsortedMap.entrySet()
            .stream()
            .sorted(Map.Entry.comparingByValue())
            .collect(Collectors.toList());

        // Create a new map from the sorted list of map entries
        Map<Integer, String> sortedMap = new LinkedHashMap<>();
        for (Map.Entry<Integer, String> entry : sortedEntries) {
            sortedMap.put(entry.getKey(), entry.getValue());
        }

        // Print the sorted map
        System.out.println("Sorted Map by Values: " + sortedMap);
    }
}

Output

Sorted Map by Values: {1=one, 2=two, 3=three}

Summary

In this tutorial, we learned How to Sort a Map by Values in Java language with well detailed examples.

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How to Sort a Map by Values in Java - Step by Step Examples