Deque interface in java

Deque interface:

Deque interface represents a double-ended-queue. A deque represents a linear collection of elements that support insertion, retrieval and removal of elements at both ends.

Deques can be used both as FIFO (first-in, first-out) and LIFO (last-in, first-out). In a deque all new elements can be inserted, retrieved and removed at both ends.

Commonly used methods of Deque interface:

1. addFirst(Object obj): Inserts the specified element at the front of this deque.

Syntax: public void addFirst(Object obj)

2. addLast(Object obj): Inserts the specified element at the end of this deque.

Syntax: public void addLast(Object obj)

3. offerFirst(Object obj): Inserts the specified element at the front of this deque. Returns true if the element was added to this deque, else false.

Syntax: public boolean offerFirst(Object obj)

4. offerLast(Object obj): Inserts the specified element at the end of this deque. Returns true if the element was added to this deque, else false.

Syntax: public boolean offerLast(Object obj)

5. removeFirst(): Returns and removes the first element of this deque.  It throws an exception if this deque is empty.

Syntax: public Object removeFirst()

6. removeLast(): Returns and removes the last element of this deque.  It throws an exception if this deque is empty.

Syntax: public Object removeLast()

7. pollFirst(): Returns and removes the first element of this deque. Returns null if this deque is empty.

Syntax: public Object pollFirst()

8. pollLast(): Returns and removes the last element of this deque.  Returns null if this deque is empty.

Syntax: public Object pollLast()

9. getFirst(): Returns but does not removes the first element of this deque.  It throws an exception if this deque is empty.

Syntax: public Object getFirst()

10. getLast(): Returns but does not removes the last element of this deque.  It throws an exception if this deque is empty.

Syntax: public Object getLast()

11. peekFirst(): Returns but does not removes the first element of this deque. Returns null if this deque is empty.

Syntax: public Object peakFirst()

12. peekLast(): Returns but does not removes the last element of this deque.  Returns null if this deque is empty.

Syntax: public Object peekLast()

13. removeFirstOccurrence(): Removes the first occurrence of the specified element from this deque. Returns true if specified element is removed from this deque otherwise returns false.

Syntax: public boolean removeFirstOccurrence()

14. removeLastOccurrence(): Removes the last occurrence of the specified element from this deque. Returns true if specified element is removed from this deque otherwise returns false.

Syntax: public boolean removeLastOccurrence()

 A simple example of ArrayDeque class to explain few methods of Deque interface.

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
 
/**
 * This class is used to show the ArrayDeque functionality.
 * @author w3schools
 */
public class ArrayDequeTest {
	public static void main(String args[]){
		//Create ArrayDeque  object.
		Deque arrayDeque  = new ArrayDeque();
 
		//Add objects to the ArrayDeque.
		arrayDeque.add("Gourav");
		arrayDeque.add("Neeraj");
		arrayDeque.add("Deepak");
		arrayDeque.add("Mohan");
		arrayDeque.add("Parmender");
 
		//Print the ArrayDeque object.
		System.out.println("ArrayDeque elements:");
		System.out.println(arrayDeque);
 
		//Print the ArrayDeque elements using iterator.
		Iterator iterator1=arrayDeque.iterator();
		System.out.println("ArrayDeque elements " +
				"using iterator:");
		while(iterator1.hasNext()){  
		   System.out.println(iterator1.next());  
		}
 
		//Print the first element of the ArrayDeque.
		System.out.println("First element: " 
				+ arrayDeque.getFirst());
 
		//Print the last element of the ArrayDeque.
		System.out.println("Last element: " 
				+ arrayDeque.getLast());
 
		//Remove the first element of the ArrayDeque.
		arrayDeque.pollFirst();
 
		//Remove the last element of the ArrayDeque.
		arrayDeque.pollLast();
 
		//Print the ArrayDeque object.
		System.out.println("ArrayDeque elements " +
				"after manipulation:");
		System.out.println(arrayDeque);
 
		//Print the ArrayDeque elements using iterator.
		Iterator iterator2=arrayDeque.iterator();
		System.out.println("ArrayDeque elements after " +
				"manipulation using iterator:");
		while(iterator2.hasNext()){  
		   System.out.println(iterator2.next());  
		}
	}
}

ArrayDeque elements:
[Gourav, Neeraj, Deepak, Mohan, Parmender]
ArrayDeque elements using iterator:
Gourav
Neeraj
Deepak
Mohan
Parmender
First element: Gourav
Last element: Parmender
ArrayDeque elements after manipulation:
[Neeraj, Deepak, Mohan]
ArrayDeque elements after manipulation using iterator:
Neeraj
Deepak
Mohan