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Sorting a HashMap according to keys in Java
As we know that Hash map in Java does not maintain insertion order either by key or by order.Also it does not maintain any other order while adding entries to it.
But Java provide another API named as TreeMap which maintain its insertion order sorted according to the natural ordering of its keys.So in order to sort our given Hash map according to keys we would insert our map into a tree map which by default insert according to key sorting.After insertion we would transverse same tree map which is sorted and is our resultant sorted map.
Example
import java.util.HashMap;
import java.util.TreeMap;
public class HashMapSortByKey {
public static void main(String[] args) {
HashMap<String,Integer> hMap = new HashMap<>();
TreeMap<String,Integer> sortedMap = new TreeMap<>();
hMap.put("Akshay",5);
hMap.put("Veer",8);
hMap.put("Guang",3);
hMap.put("Bakshi",7);
hMap.put("TomTom",2);
hMap.put("Chang",10);
hMap.put("Sandy",1);
sortedMap = sortByKey(hMap);
System.out.println(sortedMap);
}
public static TreeMap<String,Integer> sortByKey(HashMap<String,Integer> mapToSort) {
TreeMap<String,Integer> sortedMap = new TreeMap<>();
sortedMap.putAll(mapToSort);
return sortedMap;
}
}Output
myCSV.csv file created with following text
{Akshay=5, Bakshi=7, Chang=10, Guang=3, Sandy=1, TomTom=2, Veer=8}
Updated on: 25-Jun-2020
1K+ Views
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