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TreeSet comparator() Method in Java
  • Last Updated : 26 Nov, 2018

The java.util.TreeSet.comparator() method shares an important function of setting and returning the comparator that can be used to order the elements in a TreeSet. The method returns Null value if the set follows the natural ordering pattern of the elements.

Syntax:

comp_set = (TreeSet)tree_set.comparator()

Parameters: The method does not take any parameters.

Return Value: The method returns the comparator set used to order the elements of the set in a specific order. It returns a Null value if the set follows the default or natural ordering pattern.

Below are the programs illustrating the use of java.util.TreeSet.comparator() method:
Program 1: When using natural ordering of the elements:






// Java code to illustrate comparator()
import java.util.*;
  
public class Tree_Set_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeSet
        TreeSet<Integer> tree_set = new TreeSet<Integer>();
  
        // Adding elemetns to the set
        tree_set.add(20);
        tree_set.add(24);
        tree_set.add(30);
        tree_set.add(35);
        tree_set.add(45);
        tree_set.add(50);
  
      System.out.println("Tree Set values are: "+ tree_set);
  
      // Creating a comparator
      Comparator comp = tree_set.comparator();
        
      // Displaying the comparator values
      System.out.println("Since the Comparator value is: "+ comp);
      System.out.println("it follows natural ordering");
   }
}
Output:
Tree Set values are: [20, 24, 30, 35, 45, 50]
Since the Comparator value is: null
it follows natural ordering

Program 2: When using a specific comparator.




// Java code to illustrate the use of comparator()
import java.util.Comparator;
import java.util.TreeSet;
   
class The_Comparator implements Comparator<String> {
    public int compare(String str1, String str2)
    {
        String first_Str;
        String second_Str;
        first_Str = str1;
        second_Str = str2;
        return second_Str.compareTo(first_Str);
    }
}
   
public class Tree_Set_Demo {
    public static void main(String[] args)
    {
        TreeSet<String> tree_set = new TreeSet<String>(new 
        The_Comparator());
   
        tree_set.add("G");
        tree_set.add("E");
        tree_set.add("E");
        tree_set.add("K");
        tree_set.add("S");
        tree_set.add("4");
        System.out.println("Set before using the comparator: "+
        tree_set);
   
        System.out.println("The elements sorted in descending"+
        "order:");
        for (String element : tree_set)
            System.out.print(element + " ");
    }
}
Output:
Set before using the comparator: [S, K, G, E, 4]
The elements sorted in descendingorder:
S K G E 4

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