Home Communities
IT Knowledge
Inspiration
Languages
EN

# Java - sort HashMap by keys

7 points
Created by:
347

Short solution:

``````Map<String, Integer> map = new HashMap<>();
// put key / value to map

// to sort map we use tree map and default String comparator
Map<String, Integer> sortedMap = new TreeMap<>();
sortedMap.putAll(map);

sortedMap.forEach((key, value) -> {
System.out.println("Key: " + key + ", Value : " + value);
});``````

Another short solution:

``````Map<String, Integer> map = new HashMap<>();
// put key / value to map

List<String> sortedKeys = new ArrayList<>(map.keySet());
Collections.sort(sortedKeys);

// we iterate over sorted keys and get from map in sorted order
for (String key : sortedKeys) {
Integer value = map.get(key);
System.out.println("Key: " + key + ", Value : " + value);
}``````

## 1. Sort HashMap by keys using TreeMap

``````import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

public class Example1 {

public static void main(String[] args) {

Map<String, Integer> map = new HashMap<>();
map.put("YY", 3);
map.put("ZZ", 4);
map.put("CC", 2);
map.put("AA", 1);

System.out.println("Unsorted:");
map.forEach((key, value) -> {
System.out.println("Key: " + key + ", Value : " + value);
});

System.out.println("---------");

// to sort map we use tree map and default String comparator
Map<String, Integer> sortedMap = new TreeMap<>();
sortedMap.putAll(map);

System.out.println("Sorted:");
sortedMap.forEach((key, value) -> {
System.out.println("Key: " + key + ", Value : " + value);
});
}
}``````

Output:

``````Unsorted:
Key: YY, Value : 3
Key: ZZ, Value : 4
Key: CC, Value : 2
Key: AA, Value : 1
---------
Sorted:
Key: AA, Value : 1
Key: CC, Value : 2
Key: YY, Value : 3
Key: ZZ, Value : 4``````

## 2. Sort HashMap by keys using sorted list

``````import java.util.*;

public class Example2 {

public static void main(String[] args) {

Map<String, Integer> map = new HashMap<>();
map.put("YY", 3);
map.put("ZZ", 4);
map.put("CC", 2);
map.put("AA", 1);

System.out.println("Unsorted:");
map.forEach((key, value) -> {
System.out.println("Key: " + key + ", Value : " + value);
});

System.out.println("---------");

List<String> sortedKeys = new ArrayList<>(map.keySet());
Collections.sort(sortedKeys);

System.out.println("Sorted:");
// we iterate over sorted keys and get from map in sorted order
for (String key : sortedKeys) {
Integer value = map.get(key);
System.out.println("Key: " + key + ", Value : " + value);
}
}
}``````

Output:

``````Unsorted:
Key: YY, Value : 3
Key: ZZ, Value : 4
Key: CC, Value : 2
Key: AA, Value : 1
---------
Sorted:
Key: AA, Value : 1
Key: CC, Value : 2
Key: YY, Value : 3
Key: ZZ, Value : 4``````

Join to our subscribers to be up to date with content, news and offers.