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TreeMap comparator() method in Java with Examples

  • Last Updated : 08 Jun, 2021

The comparator() method of java.util.TreeMap class is used to return the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys.
Syntax: 
 

public Comparator comparator()

Return Value: This method returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys
Below are the examples to illustrate the descendingIterator() method
Example 1: For Natural ordering 
 

Java




// Java program to demonstrate
// comparator() method for natural ordering
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of TreeMap
            NavigableMap<Integer, String>
                treemap = new TreeMap<Integer, String>();
 
            // populating tree map
            treemap.put(1, "one");
            treemap.put(2, "two");
            treemap.put(3, "three");
            treemap.put(4, "four");
            treemap.put(5, "five");
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting used Comparator in the map
            // using comparator() method
            Comparator comp = treemap.comparator();
 
            // printing the comparator value
            System.out.println("Comparator value: "
                               + comp);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
Output: 
TreeMap: {1=one, 2=two, 3=three, 4=four, 5=five}
Comparator value: null

 

Example 2: For Reverse ordering 
 

Java




// Java program to demonstrate
// comparator() method
// for reverse ordering
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of TreeMap
            NavigableMap<Integer, String>
                treemap = new TreeMap<Integer, String>(
                    Collections.reverseOrder());
 
            // populating tree map
            treemap.put(1, "one");
            treemap.put(2, "two");
            treemap.put(3, "three");
            treemap.put(4, "four");
            treemap.put(5, "five");
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting used Comparator in the map
            // using comparator() method
            Comparator comp = treemap.comparator();
 
            // printing the comparator value
            System.out.println("Comparator value: " + comp);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
Output: 



TreeMap: {5=five, 4=four, 3=three, 2=two, 1=one}
Comparator value: java.util.Collections$ReverseComparator@232204a1

 

Output: 
 

Comparator value: java.util.Collections$ReverseComparator@232204a1

 

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