Deque descendingIterator() method in Java

The descendingIterator(E e) method of Deque Interface returns an iterator over the elements in this deque in a reverse sequential order. The elements will be returned in order from last(tail) to first(head). The returned iterator is a “weakly consistent” iterator.

Syntax:

Iterator descendingIterator()

Parameters: This method does not accept any parameter.

Return Value: This method returns an iterator over the elements in this deque in a proper sequence

Below programs illustrate the descendingIterator() method in Java:

Program 1: With the help of LinkedList.

// Java code to illustrate descendingIterator()
// method of Deque in Java
import java.util.*;

public class GFG {
    public static void main(String args[])
    {
        // Creating an empty Deque
        Deque<String> de_que = new LinkedList<String>();

        // Use add() method to add elements into the Queue
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");

        // Call iterator() method of deque
        Iterator iteratorVals = de_que.iterator();

        // Print elements of iterator
        // created from PriorityBlockingQueue
        System.out.println("The iterator values"
                           + " of deque are:");

        // prints the elements using an iterator
        while (iteratorVals.hasNext()) {
            System.out.println(iteratorVals.next());
        }
    }
}

Output:

The iterator values of deque are:
Welcome
To
Geeks
4
Geeks

Program 2:

// Java code to illustrate descendingIterator()
// method of Deque in Java
import java.util.*;

public class GFG {
    public static void main(String args[])
    {
        // Creating an empty Deque
        Deque<Integer> de_que = new LinkedList<Integer>();

        // Use add() method to add elements into the Queue
        de_que.add(10);
        de_que.add(15);
        de_que.add(30);
        de_que.add(20);
        de_que.add(5);

        // Call iterator() method of deque
        Iterator iteratorVals = de_que.iterator();

        // Print elements of iterator
        // created from PriorityBlockingQueue
        System.out.println("The iterator values"
                           + " of deque are:");

        // prints the elements using an iterator
        while (iteratorVals.hasNext()) {
            System.out.println(iteratorVals.next());
        }
    }
}

Output:

The iterator values of deque are:
10
15
30
20
5

Program 3: With the help of ArrayDeque.

// Java code to illustrate descendingIterator()
// method of Deque in Java
import java.util.*;

public class GFG {
    public static void main(String args[])
    {
        // Creating an empty Deque
        Deque<String> de_que = new ArrayDeque<String>();

        // Use add() method to add elements into the Queue
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");

        // Call iterator() method of deque
        Iterator iteratorVals = de_que.iterator();

        // Print elements of iterator
        // created from PriorityBlockingQueue
        System.out.println("The iterator values"
                           + " of deque are:");

        // prints the elements using an iterator
        while (iteratorVals.hasNext()) {
            System.out.println(iteratorVals.next());
        }
    }
}

Output:

The iterator values of deque are:
Welcome
To
Geeks
4
Geeks

Program 4: With the help of LinkedBlockingDeque.

// Java code to illustrate descendingIterator()
// method of Deque in Java
import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;

public class GFG {
    public static void main(String args[])
    {
        // Creating an empty Deque
        Deque<String> de_que = new LinkedBlockingDeque<String>();

        // Use add() method to add elements into the Queue
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");

        // Call iterator() method of deque
        Iterator iteratorVals = de_que.iterator();

        // Print elements of iterator
        // created from PriorityBlockingQueue
        System.out.println("The iterator values"
                           + " of deque are:");

        // prints the elements using an iterator
        while (iteratorVals.hasNext()) {
            System.out.println(iteratorVals.next());
        }
    }
}

Output:

The iterator values of deque are:
Welcome
To
Geeks
4
Geeks

Program 5: With the help of ConcurrentLinkedDeque.

// Java code to illustrate descendingIterator()
// method of Deque in Java
import java.util.*;
import java.util.concurrent.ConcurrentLinkedDeque;

public class GFG {
    public static void main(String args[])
    {
        // Creating an empty Deque
        Deque<String> de_que = new ConcurrentLinkedDeque<String>();

        // Use add() method to add elements into the Queue
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");

        // Call iterator() method of deque
        Iterator iteratorVals = de_que.iterator();

        // Print elements of iterator
        // created from PriorityBlockingQueue
        System.out.println("The iterator values"
                           + " of deque are:");

        // prints the elements using an iterator
        while (iteratorVals.hasNext()) {
            System.out.println(iteratorVals.next());
        }
    }
}

Output:

The iterator values of deque are:
Welcome
To
Geeks
4
Geeks

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#descendingIterator–