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Java TreeMap comparator() Method with Example

TreeMap Class comparator() method: Here, we are going to learn about the comparator() method of TreeMap Class with its syntax and example.
Submitted by Preeti Jain, on February 19, 2020

TreeMap Class comparator() method

  • comparator() method is available in java.util package.
  • comparator() method is used to return the key element in this TreeMap based on the Comparator object otherwise it returns null when this TreeMap follows default ordering the key elements.
  • comparator() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
  • comparator() method does not throw an exception at the time of returning the Comparator object.


    public Comparator comparator();


  • It does not accept any parameter.

Return value:

The return type of the method is Comparator, it returns Comparator object will result in ordering the key element otherwise it returns null when this TreeMap will result in default ordering the key element.


// Java program to demonstrate the example 
// of Comparator comparator() method of TreeMap 

import java.util.*;

public class ComparatorOfTreeMap {
    public static void main(String[] args) {
        // Instantiates a TreeMap object
        NavigableMap < Integer, String > tree_map = new TreeMap < Integer, String > ();

        // By using put() method is to add
        // key-value pairs in a TreeMap
        tree_map.put(10, "C");
        tree_map.put(20, "C++");
        tree_map.put(50, "JAVA");
        tree_map.put(40, "PHP");
        tree_map.put(30, "SFDC");

        // Display TreeMap 
        System.out.println("TreeMap: " + tree_map);

        // By using comparator() method is to
        // return the comparator object
        Comparator com = tree_map.comparator();

        // Display Comparator
        System.out.println("tree_map.comparator(): " + com);


TreeMap: {10=C, 20=C++, 30=SFDC, 40=PHP, 50=JAVA}
tree_map.comparator(): null


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