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–

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