Problem Scenario
The below HashMap contains the key as the name of the person and value as the age of the person. We need to sort the hashmap using the Value (According to the age of the person).
HashMap Input
Name - Sam Age - 42
Name - John Age - 43
Name - Adam Age - 18
Name - Bob Age - 50
Name - Micheal Age - 16
Output Expected
Key : Micheal Value : 16
Key : Adam Value : 18
Key : Sam Value : 42
Key : John Value : 43
Key : Bob Value : 50
Sorting using Streams & Comparator
The sortedMap method will take the hashmap as input and using the Comparator and the Sorted method the values of the hashmap will be sorted. The sorted values will be added to the newly created LinkedHashMap. We have created the LinkedHashMap instead of the Hashmap because the LinkedHashMap will keep the insertion order and Hashmap doesn't keep the insertion order.
public Map<String, Integer> sortedMap(Map<String, Integer> map) {
return map.entrySet().stream().sorted((v1, v2) -> v1.getValue()
.compareTo(v2.getValue())).collect(Collectors.toMap
(Map.Entry::getKey, Map.Entry::getValue,
(k, v) -> k, LinkedHashMap::new));
}
Once we have sorted the values of the Hashmap we will print the sorted values in the console. Complete code changes are attached below.
HashMapSort.java
package com.sandbox.code;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.stream.Collectors;
public class HashMapSort {
public static void main(String[] args) {
Map<String, Integer> mapVal = new HashMap<>();
mapVal.put("Sam", 42);
mapVal.put("John", 43);
mapVal.put("Adam", 18);
mapVal.put("Bob", 50);
mapVal.put("Micheal", 16);
mapVal = new HashMapSort().sortedMap(mapVal);
mapVal.forEach((k, v) -> System.out.println("Key : " + k + " Value : " + v));
}
public Map<String, Integer> sortedMap(Map<String, Integer> map) {
return map.entrySet().stream().sorted((v1, v2) -> v1.getValue().compareTo(v2.getValue()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (k, v) -> k, LinkedHashMap::new));
}
}
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