NavigableSet descendingSet() method in Java

Last Updated : 29 Sep, 2018

The descendingSet() method of NavigableSet interface in Java is used to return a reverse order view of the elements contained in this set. The descending set is backed by this set, so any changes to the set are reflected in the descending set, and vice-versa. If any of the set is modified while an iteration over other set is in progress, the results of the iteration are undefined.

Syntax:

Iterator<E> descendingSet()

Where, E is the type of elements maintained by this Set container.

Parameters: This function does not accepts any parameter.

Return Value: It returns a reverse order view of the elements contained in this set.

Below programs illustrate the descendingSet() method in Java:

Program 1: NavigableSet with integer elements.

// A Java program to demonstrate
// descendingSet() method of NavigableSet
  
import java.util.NavigableSet;
import java.util.TreeSet;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        NavigableSet<Integer> ns = new TreeSet<>();
        ns.add(0);
        ns.add(1);
        ns.add(2);
        ns.add(3);
        ns.add(4);
        ns.add(5);
        ns.add(6);
  
        NavigableSet new_ns = ns.descendingSet();
  
        Iterator itr = new_ns.iterator();
  
        // Iterate over the elements using itr
        while (itr.hasNext()) {
            System.out.println("Value: " + itr.next() + " ");
        }
    }
}

Output:

Value: 6 
Value: 5 
Value: 4 
Value: 3 
Value: 2 
Value: 1 
Value: 0

Program 2: NavigableSet with string elements.

// A Java program to illustrate descendingSet()
// method of NavigableSet
import java.util.NavigableSet;
import java.util.TreeSet;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        NavigableSet<String> ns = new TreeSet<>();
        ns.add("A");
        ns.add("B");
        ns.add("C");
        ns.add("D");
        ns.add("E");
        ns.add("F");
        ns.add("G");
  
        NavigableSet new_ns = ns.descendingSet();
  
        Iterator itr = new_ns.iterator();
  
        // Iterate over the elements using itr
        while (itr.hasNext()) {
            System.out.println("Value: " + itr.next() + " ");
        }
    }
}

Output:

Value: G 
Value: F 
Value: E 
Value: D 
Value: C 
Value: B 
Value: A

Reference: https://docs.oracle.com/javase/10/docs/api/java/util/NavigableSet.html#descendingSet()

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