Java.util.ArrayDeque Class in Java | Set 1

java.util.ArrayDeque class describes an implementation of a resizable array structure which implements the Deque interface. 
Array deques has not immutable and can grow as necessary. They are not thread-safe and hence concurrent access by multiple threads is not supported unless explicitly synchronized. Null elements are invalid in this structure. Most operations run in constant time, with speed decreasing linearly as size grows. 

Declaration 

public class ArrayDeque
   extends AbstractCollection
   implements Deque, Cloneable, Serializable

Methods of ArrayDeque Class : 

1. add(Element e) : java.util.ArrayDeque.add(Element e) inserts particular element at the end of the deque. 
Syntax :

public boolean add(Element e)
Parameter
e : element to add
Return
true : if element is inserted, else no

2. addFirst(Element e) : java.util.ArrayDeque.addFirst(Element e) inserts particular element at the start of the deque. 
Syntax :

public boolean addFirst(Element e)
Parameter
e : element to add at the start
Return
true : if element is inserted, else no

3. addLast(Element e) : java.util.ArrayDeque.addLast(Element e) inserts particular element at the end of the deque. It is similar to add() method 
Syntax :

public boolean addaddLast(Element e)
Parameter
e : element to add at end
Return
true : if element is inserted, else no

4. clear() : java.util.ArrayDeque.clear() removed all deque elements. 
Syntax :

public void clear()
Parameter
-------
Return
-------

5. size() : java.util.ArrayDeque.size() returns the no. of elements in deque. 
Syntax :

public int size()
Parameter
-----
Return
no. of elements in deque.

6. clone() : java.util.ArrayDeque.clone()copies the deque. 
Syntax :

public ArrayDeque clone()
Parameter
--------
Return
copy of deque

7. contains(Obj) : java.util.ArrayDeque.contains(Obj) checks whether a deque contains the element or not 
Syntax :

public boolean contains(Object obj) 
Parameter
obj : object to be checked
Return
true, if element is +nt in the deque; else false

8. Iterator() : java.util.ArrayDeque.Iterator() returns an iterator over the deque. 
Syntax :

public Iterator Iterator()
Parameter
----------
Return
iterator over the deque.

9. descendingIterator() : java.util.ArrayDeque.descendingIterator() returns a reverse order iterator over the deque 
Syntax :

public Iterator descendingIterator()
Parameter
----------
Return
returns a reverse order iterator over the deque.

10. element() : java.util.ArrayDeque.element() returns element at the head of the deque 
Syntax :

public E element()
Parameter
------
Return
head element of the deque

11. getFirst: java.util.ArrayDeque.getFirst()returns first element of the deque 
Syntax :

public E getFirst()
Parameter
------
Return
head element of the deque

12. getLast: java.util.ArrayDeque.getLast()returns last element of the deque 
Syntax :

public E getLast()
Parameter
------
Return
last element of the deque

13. isEmpty(): java.util.ArrayDeque.isEmpty() checks whether the deque is empty or not. 
Syntax :

public boolean isEmpty()
Parameter
------
Return
true if the deque is empty; else false

14. toArray(): java.util.ArrayDeque.toArray() returns array having the elements of deque. 
Syntax :

public Object[] toArray()
Parameter
------
Return
returns array having the elements of deque.

Java Program explaining ArrayDeque class methods : 

// Java code explaining the use of ArrayDeque class methods
// add(), addFirst(), addLast(), clear(), size(), contains()
// descendingIterator(), element(), getFirst(), isEmpty(),
// toArray, Iterator(), getLast()

import java.util.*;
public class NewClass
{
    public static void main(String[] args)
    {
        // Initializing an deque
        Deque<Integer> d = new ArrayDeque<Integer>(10);

        // add() method to insert
        d.add(2);
        d.add(4);
        d.add(6);
        d.add(8);
        d.add(2);
        for (Integer element : d)
        {
            System.out.println("Element : " + element);
        }

        System.out.println("Using clear() ");
        //clear() method
        d.clear();

        // addFirst() method to insert at start
        d.addFirst(10);
        d.addFirst(20);

        // addLast() method to insert at end
        d.addLast(24);
        d.addLast(14);

        System.out.println("Above elements are removed now \n");

        //size() of ArrayDeque
        System.out.println("Size of deque : " + d.size() + "\n");
        for (Integer element : d)
        {
            System.out.println("Element : " + element);
        }

        // contains() method
        System.out.println("\nIs 10 +nt in deque : " + d.contains(10));



        // Iterator() :
        System.out.println("\nElements of deque using Iterator :");
        for(Iterator itr = d.iterator(); itr.hasNext();)
        {
            System.out.println(itr.next());
        }


        // descendingIterator() : to reverse the deque order
        System.out.println("\nElements of deque in reverse order :");
        for(Iterator dItr = d.descendingIterator(); dItr.hasNext();)
        {
            System.out.println(dItr.next());
        }

        // element() method : to get Head element
        System.out.println("\nHead Element using element(): " + d.element());

        // getFirst() method : to get Head element
        System.out.println("Head Element using getFirst(): " + d.getFirst());

        // getLast() method : to get last element
        System.out.println("Last Element using getLast(): " + d.getLast());


        // isEmpty() method :
        System.out.println("\nChecks whether deque is empty : " + d.isEmpty());

        //toArray() method :
        Object[] arr = d.toArray();
        System.out.println("\nArray Size : " + arr.length);

        System.out.print("Array elements : ");
        for(int i=0; i<arr.length ; i++)
            System.out.print(" " + arr[i]);
    }
}

Output : 

Element : 2
Element : 4
Element : 6
Element : 8
Element : 2
Using clear() 
Above elements are removed now 

Size of deque : 4

Element : 20
Element : 10
Element : 24
Element : 14

Is 10 +nt in deque : true

Elements of deque using Iterator :
20
10
24
14

Elements of deque in reverse order :
14
24
10
20

Head Element using element(): 20
Head Element using getFirst(): 20
Last Element using getLast(): 14

Checks whether deque is empty : false

Array Size : 4
Array elements :  20 10 24 14

Java.util.ArrayDeque Class in Java | Set 2