The ArrayDeque in Java provides a way to apply resizable-array in addition to the implementation of the Deque interface. It is also known as Array Double Ended Queue or Array Deck. This is a special kind of array that grows and allows users to add or remove an element from both sides of the queue.
The ArrayDeque class in Java is an implementation of the Deque interface that uses a resizable array to store its elements. This class provides a more efficient alternative to the traditional Stack class, which was previously used for double-ended operations. The ArrayDeque class provides constant-time performance for inserting and removing elements from both ends of the queue, making it a good choice for scenarios where you need to perform many add and remove operations.
Here’s an example of how you might use an ArrayDeque in Java:
Java
import java.util.ArrayDeque;
import java.util.Deque;
public class Example {
public static void main(String[] args) {
Deque<Integer> deque = new ArrayDeque<>();
deque.addFirst(1);
deque.addLast(2);
int first = deque.removeFirst();
int last = deque.removeLast();
System.out.println("First: " + first + ", Last: " + last);
}
}
|
Advantages of using ArrayDeque:
- Efficient: The ArrayDeque class provides constant-time performance for inserting and removing elements from both ends of the queue, making it a good choice for scenarios where you need to perform many add and remove operations.
- Resizable: The ArrayDeque class uses a resizable array to store its elements, which means that it can grow and shrink dynamically to accommodate the number of elements in the queue.
- Lightweight: The ArrayDeque class is a lightweight data structure that does not require additional overhead, such as linked list nodes, making it a good choice for scenarios where memory is limited.
- Thread-safe: The ArrayDeque class is not thread-safe, but you can use the Collections.synchronizedDeque method to create a thread-safe version of the ArrayDeque class.
Disadvantages of using ArrayDeque:
- Not synchronized: By default, the ArrayDeque class is not synchronized, which means that multiple threads can access it simultaneously, leading to potential data corruption.
- Limited capacity: Although the ArrayDeque class uses a resizable array to store its elements, it still has a limited capacity, which means that you may need to create a new ArrayDeque when the old one reaches its maximum size.
Few important features of ArrayDeque are as follows:
- Array deques have no capacity restrictions and they grow as necessary to support usage.
- They are not thread-safe which means that in the absence of external synchronization, ArrayDeque does not support concurrent access by multiple threads.
- Null elements are prohibited in the ArrayDeque.
- ArrayDeque class is likely to be faster than Stack when used as a stack.
- ArrayDeque class is likely to be faster than LinkedList when used as a queue.
Interfaces implemented by ArrayDeque:
The ArrayDeque class implements these two interfaces:
- Queue Interface: It is an Interface that is a FirstIn – FirstOut Data Structure where the elements are added from the back.
- Deque Interface: It is a Doubly Ended Queue in which you can insert the elements from both sides. It is an interface that implements the Queue.
ArrayDeque implements both Queue and Deque. It is dynamically resizable from both sides. All implemented interfaces of ArrayDeque in the hierarchy are Serializable, Cloneable, Iterable<E>, Collection<E>, Deque<E>, Queue<E>
Syntax: Declaration
public class ArrayDeque<E>
extends AbstractCollection<E>
implements Deque<E>, Cloneable, Serializable
Here, E refers to the element which can refer to any class, such as Integer or String class.
Now we are done with syntax now let us come up with constructors been defined for it prior before implementing to grasp it better and perceiving the output better.
- ArrayDeque(): This constructor is used to create an empty ArrayDeque and by default holds an initial capacity to hold 16 elements.
ArrayDeque<E> dq = new ArrayDeque<E>();
- ArrayDeque(Collection<? extends E> c): This constructor is used to create an ArrayDeque containing all the elements the same as that of the specified collection.
ArrayDeque<E> dq = new ArrayDeque<E>(Collection col);
- ArrayDeque(int numofElements): This constructor is used to create an empty ArrayDeque and holds the capacity to contain a specified number of elements.
ArrayDeque<E> dq = new ArrayDeque<E>(int numofElements);
Methods in ArrayDeque are as follows:
Note: Here, Element is the type of elements stored by ArrayDeque.
METHOD | DESCRIPTION |
|---|
| add(Element e) | The method inserts a particular element at the end of the deque. |
| addAll(Collection<? extends E> c) | Adds all of the elements in the specified collection at the end of this deque, as if by calling addLast(E) on each one, in the order that they are returned by the collection’s iterator. |
| addFirst(Element e) | The method inserts particular element at the start of the deque. |
| addLast(Element e) | The method inserts a particular element at the end of the deque. It is similar to the add() method |
| clear() | The method removes all deque elements. |
| clone() | The method copies the deque. |
| contains(Obj) | The method checks whether a deque contains the element or not |
| element() | The method returns element at the head of the deque |
| forEach(Consumer<? super E> action) | Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. |
| getFirst() | The method returns first element of the deque |
| getLast() | The method returns last element of the deque |
| isEmpty() | The method checks whether the deque is empty or not. |
| iterator() | Returns an iterator over the elements in this deque. |
| offer(Element e) | The method inserts element at the end of deque. |
| offerFirst(Element e) | The method inserts element at the front of deque. |
| offerLast(Element e) | The method inserts element at the end of the deque. |
| peek() | The method returns head element without removing it. |
| poll() | The method returns head element and also removes it |
| pop() | The method pops out an element for stack represented by deque |
| push(Element e) | The method pushes an element onto stack represented by deque |
| remove() | The method returns head element and also removes it |
| remove(Object o) | Removes a single instance of the specified element from this deque. |
| removeAll(Collection<?> c) | Removes all of this collection’s elements that are also contained in the specified collection (optional operation). |
| removeFirst() | The method returns the first element and also removes it |
| removeFirstOccurrence(Object o) | Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail). |
| removeIf(Predicate<? super Element> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
| removeLast() | The method returns the last element and also removes it |
| removeLastOccurrence(Object o) | Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail). |
| retainAll(Collection<?> c) | Retains only the elements in this collection that are contained in the specified collection (optional operation). |
| size() | Returns the number of elements in this deque. |
| spliterator() | Creates a late-binding and fail-fast Spliterator over the elements in this deque. |
| toArray() | Returns an array containing all of the elements in this deque in proper sequence (from first to the last element). |
| toArray(T[] a) | Returns an array containing all of the elements in this deque in proper sequence (from first to the last element); the runtime type of the returned array is that of the specified array. |
Methods inherited from class java.util.AbstractCollection
Method | Action Performed |
|---|
| containsAll(Collection c) | Returns true if this collection contains all of the elements in the specified collection. |
| toString() | Returns a string representation of this collection. |
Methods inherited from interface java.util.Collection
Method | Action Performed |
|---|
| containsAll(Collection c) | Returns true if this collection contains all of the elements in the specified collection. |
| equals() | Compares the specified object with this collection for equality. |
| hashcode() | Returns the hash code value for this collection. |
| parallelStream() | Returns a possibly parallel Stream with this collection as its source. |
| stream() | Returns a sequential Stream with this collection as its source. |
| toArray(IntFunction<T[]> generator) | Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array. |
Methods declared in interface java.util.Deque
Method | Action Performed |
|---|
| descendingIterator() | Returns an iterator over the elements in this deque in reverse sequential order. |
| peekFirst() | Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty. |
| peekLast() | Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty. |
| pollFirst() | Retrieves and removes the first element of this deque, or returns null if this deque is empty. |
| pollLast() | Retrieves and removes the last element of this deque, or returns null if this deque is empty. |
Example
Java
import java.util.*;
public class GGFG {
public static void main(String[] args)
{
Deque<Integer> de_que = new ArrayDeque<Integer>(10);
de_que.add(10);
de_que.add(20);
de_que.add(30);
de_que.add(40);
de_que.add(50);
for (Integer element : de_que) {
System.out.println("Element : " + element);
}
System.out.println("Using clear() ");
de_que.clear();
de_que.addFirst(564);
de_que.addFirst(291);
de_que.addLast(24);
de_que.addLast(14);
System.out.println(
"Above elements are removed now");
System.out.println(
"Elements of deque using Iterator :");
for (Iterator itr = de_que.iterator();
itr.hasNext();) {
System.out.println(itr.next());
}
System.out.println(
"Elements of deque in reverse order :");
for (Iterator dItr = de_que.descendingIterator();
dItr.hasNext();) {
System.out.println(dItr.next());
}
System.out.println(
"\nHead Element using element(): "
+ de_que.element());
System.out.println("Head Element using getFirst(): "
+ de_que.getFirst());
System.out.println("Last Element using getLast(): "
+ de_que.getLast());
Object[] arr = de_que.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]);
System.out.println("\nHead element : "
+ de_que.peek());
System.out.println("Head element poll : "
+ de_que.poll());
de_que.push(265);
de_que.push(984);
de_que.push(2365);
System.out.println("Head element remove : "
+ de_que.remove());
System.out.println("The final array is: " + de_que);
}
}
|
OutputElement : 10
Element : 20
Element : 30
Element : 40
Element : 50
Using clear()
Above elements are removed now
Elements of deque using Iterator :
291
564
24
14
Elements of deque in reverse order :
14
24
564
291
Head Element using element(): 291
Head Element using getFirst(): 291
Last Element using getLast(): 14
Array Size : 4
Array elements : 291 564 24 14
Head element : 291
Head element poll : 291
Head element remove : 2365
The final array is: [984, 265, 564, 24, 14]
If there is some lag in clarity in this example, if so then we are proposing various operations on the ArrayDeque class Let’s see how to perform a few frequently used operations on the ArrayDeque to get a better understanding of the operations that we have used above to illustrate Array Deque as a whole.
- Adding operation
- Accessing operation
- Removing operations
- Iterating through the Deque
Let us go through each of the operations by implementing alongside by providing clean java program as follows:
Operation 1: Adding Elements
In order to add an element to the ArrayDeque, we can use the methods add(), addFirst(), addLast(), offer(), offerFirst(), offerLast() methods.
Example
Java
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Deque<String> dq = new ArrayDeque<String>();
dq.add("The");
dq.addFirst("To");
dq.addLast("Geeks");
dq.offer("For");
dq.offerFirst("Welcome");
dq.offerLast("Geeks");
System.out.println("ArrayDeque : " + dq);
}
}
|
OutputArrayDeque : [Welcome, To, The, Geeks, For, Geeks]
Operation 2: Accessing the Elements
After adding the elements, if we wish to access the elements, we can use inbuilt methods like getFirst(), getLast(), etc.
Example
Java
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String args[])
{
ArrayDeque<String> de_que
= new ArrayDeque<String>();
de_que.add("Welcome");
de_que.add("To");
de_que.add("Geeks");
de_que.add("4");
de_que.add("Geeks");
System.out.println("ArrayDeque: " + de_que);
System.out.println("The first element is: "
+ de_que.getFirst());
System.out.println("The last element is: "
+ de_que.getLast());
}
}
|
OutputArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The first element is: Welcome
The last element is: Geeks
Operation 3. Removing Elements
In order to remove an element from a deque, there are various methods available. Since we can also remove from both the ends, the deque interface provides us with removeFirst(), removeLast() methods. Apart from that, this interface also provides us with the poll(), pop(), pollFirst(), pollLast() methods where pop() is used to remove and return the head of the deque. However, poll() is used because this offers the same functionality as pop() and doesn’t return an exception when the deque is empty. These sets of operations are as listed below as follows:
Example
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Deque<String> dq = new ArrayDeque<String>();
dq.add("One");
dq.addFirst("Two");
dq.addLast("Three");
System.out.println("ArrayDeque : " + dq);
System.out.println(dq.pop());
System.out.println(dq.poll());
System.out.println(dq.pollFirst());
System.out.println(dq.pollLast());
}
}
|
OutputArrayDeque : [Two, One, Three]
Two
One
Three
null
Operation 4: Iterating through the Deque
Since a deque can be iterated from both directions, the iterator method of the deque interface provides us two ways to iterate. One from the first and the other from the back. These sets of operations are listed below as follows:
Example
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Deque<String> dq = new ArrayDeque<String>();
dq.add("For");
dq.addFirst("Geeks");
dq.addLast("Geeks");
dq.add("is so good");
for (Iterator itr = dq.iterator(); itr.hasNext();) {
System.out.print(itr.next() + " ");
}
System.out.println();
for (Iterator itr = dq.descendingIterator();
itr.hasNext();) {
System.out.print(itr.next() + " ");
}
}
}
|
OutputGeeks For Geeks is so good
is so good Geeks For Geeks
Related Articles:
Reference Book:
“Java Generics and Collections” by Maurice Naftalin and Philip Wadler is a comprehensive guide to the Java Collections Framework and generics, including the ArrayDeque class. This book covers the basics of the Collections Framework, explains how to use collections and generics in practice, and provides tips and best practices for writing correct and efficient code. If you’re looking to learn more about the ArrayDeque class and the Java Collections Framework in general, this book is an excellent resource.