Java: Sort keys in Tree Map by using comparator

Last update on May 23 2025 13:08:14 (UTC/GMT +8 hours)

7. Sort TreeMap Keys with Comparator

Write a Java program to sort keys in a Tree Map by using a comparator.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example7 {  
    public static void main(String args[]){  
  TreeMap<String,String> tree_map1 = new TreeMap<String,String>(new sort_key());
   // Put elements to the map 
  tree_map1.put("C2", "Red");
  tree_map1.put("C4", "Green");
  tree_map1.put("C3", "Black");
  tree_map1.put("C1", "White"); 
  System.out.println(tree_map1); 
    }
}
 class sort_key implements Comparator<String>{
     @Override
    public int compare(String str1, String str2) {
        return str1.compareTo(str2);
    }
     
}

Sample Output:

{C1=White, C2=Red, C3=Black, C4=Green}

For more Practice: Solve these Related Problems:

Write a Java program to create a TreeMap with a custom comparator that sorts keys in descending order.
Write a Java program to sort a TreeMap’s keys by their string lengths using a custom comparator.
Write a Java program to implement a TreeMap with a reversed natural order using Collections.reverseOrder().
Write a Java program to compare a TreeMap’s natural ordering with one sorted by a custom comparator and print both orders.

Go to:

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Java Code Editor:

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