ConcurrentSkipListSet descendingSet() method in Java

The descendingSet() method of java.util.concurrent.ConcurrentSkipListSet is an in-built function in Java which returns a reverse order view of the elements contained in this set. The descending set is backed by this set, so changes to the set are reflected in the descending set, and vice-versa.

Syntax:

ConcurrentSkipListSet.descendingSet()

Return Value: The function returns a NavigableSet which is a reverse order view of this set.

Below programs illustrate the ConcurrentSkipListSet.Set() method:

Program 1:

// Java Program Demonstrate descendingSet()
// method of ConcurrentSkipListSet */
import java.util.NavigableSet;
import java.util.Iterator;
import java.util.concurrent.ConcurrentSkipListSet;

class ConcurrentSkipListSetIteratorExample1 {
    public static void main(String[] args)
    {

        // Initializing the set
        ConcurrentSkipListSet<Integer>
            set = new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        set.add(10);
        set.add(35);
        set.add(20);
        set.add(25);

        // Printing the elements of the set
        System.out.println("Contents of the set: " + set);

        // Creating a descending set object
        NavigableSet<Integer> des_set = set.descendingSet();

        // Printing the elements of the descending set
        System.out.println("Contents of the descending set: "
                                                  + des_set);
    }
}

Output:

Contents of the set: [10, 20, 25, 35]
Contents of the descending set: [35, 25, 20, 10]

Program 2: Program demonstrating change in the original set while insertion of elements in the descending set.

// Java Program Demonstrate descendingSet()
// method of ConcurrentSkipListSet */
import java.util.NavigableSet;
import java.util.Iterator;
import java.util.concurrent.ConcurrentSkipListSet;

class ConcurrentSkipListSetIteratorExample2 {
    public static void main(String[] args)
    {

        // Initializing the set
        ConcurrentSkipListSet<String>
            set = new ConcurrentSkipListSet<String>();

        // Adding elements to this set
        set.add("bob");
        set.add("alex");
        set.add("eric");
        set.add("chuck");

        // Creating a descending object
        NavigableSet<String> des_set = set.descendingSet();

        // Adding elements to the descending set and also to the set
        des_set.add("drake");
        des_set.add("fred");

        // Printing the elements of the set
        System.out.println("Contents of the set: " + set);

        // Printing the elements of the descending set
        System.out.println("Contents of the descending set: "
                                                  + des_set);
    }
}

Output:

Contents of the set: [alex, bob, chuck, drake, eric, fred]
Contents of the descending set: [fred, eric, drake, chuck, bob, alex]

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#descendingSet–