HashMap<K, V> is a Java Collection and is a part of java.util package. It provides the basic implementation of the Map interface of Java. It stores the data in the form of Key, Value pairs, where the keys must be unique but there is no restriction for values. If we try to insert the duplicate key, it will replace the element of the corresponding key.
HashMap Sorting by Values
The idea is to store the entry set in a list and then sort the list based on values using the Collections.sort() method with the help of Comparator. Then fetch the value for each key from the list and then display the result.
Example
Java
// Java program to sort Hashmap based on valuesÂ
import java.lang.*;import java.util.*;Â
public class GFG {Â
    // function to sort hashmap based on values    public static HashMap<String, Integer>    sortByValue(HashMap<String, Integer> hm)    {        // Creating a list from elements of HashMap        List<Map.Entry<String, Integer> > list            = new LinkedList<Map.Entry<String, Integer> >(                hm.entrySet());Â
        // Sorting the list using Collections.sort() method        // using Comparator        Collections.sort(            list,            new Comparator<Map.Entry<String, Integer> >() {                public int compare(                    Map.Entry<String, Integer> object1,                    Map.Entry<String, Integer> object2)                {                    return (object1.getValue())                        .compareTo(object2.getValue());                }            });Â
        // putting the data from sorted list back to hashmap        HashMap<String, Integer> result            = new LinkedHashMap<String, Integer>();        for (Map.Entry<String, Integer> me : list) {            result.put(me.getKey(), me.getValue());        }Â
        // returning the sorted HashMap        return result;    }Â
    // Driver Code    public static void main(String[] args)    {        // creating object of HashMap class        HashMap<String, Integer> hashmap            = new HashMap<String, Integer>();Â
        // inserting key-value pair into hashmap        hashmap.put("five", 5);        hashmap.put("seven", 7);        hashmap.put("three", 3);        hashmap.put("nine", 9);        hashmap.put("zero", 0);        hashmap.put("eight", 8);Â
        // sorting the HashMap based on values        Map<String, Integer> map = sortByValue(hashmap);Â
        // print the sorted hashmap(based on values)        for (Map.Entry<String, Integer> entry :             map.entrySet()) {            System.out.println("Key : " + entry.getKey()                               + ", Value : "                               + entry.getValue());        }    }} |
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Output
Key : zero, Value : 0 Key : three, Value : 3 Key : five, Value : 5 Key : seven, Value : 7 Key : eight, Value : 8 Key : nine, Value : 9
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HashMap Sorting by Keys
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The idea is to put all data of HashMap into an ArrayList.Then extract all the keys of HashMap into an ArrayList. Next, sort the extracted keys using the Collections.sort() method, and then for each key extract its value using the get() method. Finally, the map is sorted according to its keys.
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Example
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Java
// Java Code to sort Map by key valueimport java.util.*;class GFG {Â
    // This map stores unsorted values    static HashMap<Integer, String> m = new HashMap<>();Â
    // Function to sort map by Key    public static void sortMapByKey()    {        ArrayList<Integer> sortKeys            = new ArrayList<Integer>(m.keySet());Â
        Collections.sort(sortKeys);Â
        // Getting value for each key and displaying        // results.        for (Integer x : sortKeys)            System.out.println("Key = " + x                               + ", Value = " + m.get(x));    }Â
    // Driver Code    public static void main(String args[])    {        // putting values in the Map        m.put(7, "seven");        m.put(5, "five");        m.put(1, "one");        m.put(3, "three");        m.put(9, "nine");Â
        // Calling the function to sortMapByKey to        // perform sorting based on keys        sortMapByKey();    }} |
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Output
Key = 1, Value = one Key = 3, Value = three Key = 5, Value = five Key = 7, Value = seven Key = 9, Value = nine
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