New Tutorials:   TKINTER    KOTLIN    JAVASCRIPT    SASS/SCSS    PL/SQL
See the Tutorial List

Deque Interface


In Java, the Deque interface is under java.util.Deque and it is a subtype of java.util.Queue interface. A Deque is a double-ended queue that means addition and deletion of the elements can be done from both the ends. The Deque can be used as a Queue or as Stack i.e First-in-first-out or Last-in-last-out.

Below is the hierarchy of Deque interface

deque-interface-heirarchy

Below are the methods of Deque interface

S.No. Method Description
1 add(element) It is used for adding elements at the tail of the Deque.
2 addFirst(element) It is used for adding elements at the head of the Deque.
3 addLast(element) It is used for adding elements at the tail of the Deque.
4 offer(element) It is used to add an element at the tail and returns a Boolean value if added successfully.
5 offerFirst(element) It is used to addan element at the head and returns a Boolean value if added successfully.
6 offerLast(element) It is used to addan element at the tail and returns a Boolean value if added successfully.
7 iterator() It is used to iterate the deque.
8 descendingIterator() It is used to iterate for the reverse order in the deque.
9 push(element) It is used for adding elements at the head of the deque.
10 pop(element) It is used for removing elements from the head of the deque.
11 removeFirst() It is used for removing elements from the head of the deque.
12 removeLast() It is used for removing elements from the tail of the deque
13 poll() It is used to get and remove the first element from the deque. If the deque is empty then it returns null.
14 pollFirst() It is used to get and remove the first element from the deque. If the deque is empty then it returns null.
15 pollLast() It is used to get and remove the last element from the deque. If the deque is empty then it returns null.
16 peek() It is used for removing the head of the deque.
17 peekFirst() It is used for removing the head of the deque.
18 peekLast() It is used for removing the tail of the deque.

Example:

	
import java.util.*; 

public class DequeDemo1 
{ 
    public static void main(String[] args) 
    { 
Dequeobj = new LinkedList(); 

obj.add("A 1 (Tail)");
obj.addFirst("B 2 (Head)"); 
obj.addLast("C 3 (Tail)"); 
obj.push("D 4 (Head)"); 
obj.offer("E 5 (Tail)"); 
obj.offerFirst("F 6 (Head)"); 
obj.offerLast("G 7 (Tail)"); 
	System.out.println("*****************************************************************************");
System.out.println(obj + "\n");

	System.out.println("*****************************************************************************"); 
System.out.println("Standard Iterator"); 
        Iterator iterator = obj.iterator(); 
        while (iterator.hasNext()) 
System.out.println("\t" + iterator.next()); 

        Iterator reverse = obj.descendingIterator();

	System.out.println("*****************************************************************************"); 
System.out.println("Reverse Iterator"); 
        while (reverse.hasNext()) 
System.out.println("\t" + reverse.next()); 

	System.out.println("*****************************************************************************");
System.out.println("Peek " + obj.peek()); 

	System.out.println("*****************************************************************************");
System.out.println("After peek: " + obj); 

	System.out.println("*****************************************************************************");
System.out.println("Pop " + obj.pop()); 

	System.out.println("*****************************************************************************");
System.out.println("After pop: " + obj); 

	System.out.println("*****************************************************************************");
System.out.println("Contains element 3: " + obj.contains("Element 3 (Tail)")); 

obj.removeFirst(); 
obj.removeLast(); 

	System.out.println("*****************************************************************************");
System.out.println("Deque after removing " + "first and last: " + obj); 
    } 
}
	

deque-example