Understanding ArrayDeque class in java

ArrayDeque class

 
ArrayDeque is a resizable array implementation of the Deque interface.
 
It creates a dynamic array and has no size restriction.
 
ArrayDeque class extends AbstractCollection and implements the Deque interface.
 
 

Constructors of ArrayDeque class

 
Here are the constructors of the ArrayDeque class:
 

ArrayDeque()

 
Creates an empty array deque with initial capacity to hold 16 elements.
 

ArrayDeque(int numElements)

Creates an empty array deque with initial capacity as provided.
 

ArrayDeque(Collection c)

 
Creates array deque with elements of specified collection, in order of return of the collection’s iterator

ArrayDeque common methods

 
ArrayDeque has no methods of its own.
 
Here are the frequently used methods with ArrayDeque:
 
 

add(E e), offer(E e), addLast(E e), offerLast(E e)

 
Inserts the specified element at the end of this deque.
 

addFirst(E e), offerFirst(E e), push(E e)

 
Inserts the specified element at the front of this deque.

peek(), peekFirst()

 
Retieves, but does not remove the first element of the deque

pop(), removeFirst()

 
Retrieves and removes the first element of this deque.
 

remove(Object o)

 
Removes a single instance of the specified element from this deque. If the deque does not contain the element, it is unchanged.

remove()

 
Retrieves and removes first element from deque.
 
This method differs from poll only in that it throws an exception if this deque is empty.
 

poll()

 
Retrieves and removes first element from deque.
 
Returns NULL if deque is empty.
 
 

Example of using ArrayDeque class

 
Here is an example of ArrayDeque class and its methods.
 

package com.topjavatutorial;

import java.util.ArrayDeque;

public class ArrayDequeDemo {

  public static void main(String[] args) {

    ArrayDeque<String> adq = new ArrayDeque<String>();
    
    adq.add("C"); // adds C 
    adq.push("B"); // adds B at front of deque
    adq.addFirst("A"); // adds A at front of deque
    adq.offer("D"); // adds D at end of queue
    
    //adq at this point = [A, B, C, D]
    
    System.out.print(adq.remove()); // removes A from top and returns it
    
    System.out.print(adq.poll()); // removes B from top and returns it
    
    while(adq.peek() != null)
      System.out.print(adq.pop()); // removes element from top and returns it
  }

}

 
In this program, we add the Strings [A, B, C, D] to the ArrayDeque using methods add(), push(), addFirst() and offer().
 
Then, these elements are removed and returned using remove(), poll(), pop() methods.
 
Running this program will output :

A B C D

You may also like following articles on Java Collections:

• ConcurrentHashMap in Java
• TreeMap in java
• LinkedHashMap in java
• WeakHashMap in java
• IdentityHashMap in java
• HashMap in java
• HashSet in java
• LinkedList in java
• ArrayList in java

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