The ConcurrentLinkedDeque class in Java is a part of the Java Collection Framework and implements the Collection interface and the AbstractCollection class. It belongs to java.util.concurrent package. It is used to implement Deque with the help of LinkedList concurrently.
Features of ConcurrentLinkedDeque
- Iterators and spliterators are weakly consistent.
- Concurrent insertion, removal, and access operations execute safely across multiple threads.
- It does not permit null elements.
- size() method is not implemented in constant time. Because of the asynchronous nature of these deques, determining the current number of elements requires a traversal of the elements.
The ConcurrentLinkedDeque class in Java is a thread-safe implementation of the Deque interface that uses a linked list to store its elements. The ConcurrentLinkedDeque class provides a scalable and high-performance alternative to the ArrayDeque class, particularly in scenarios where multiple threads access the deque concurrently. The ConcurrentLinkedDeque class provides methods for inserting and removing elements from both ends of the deque, and for retrieving elements from the head and tail of the deque, 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 a ConcurrentLinkedDeque in Java:
Java
import java.util.concurrent.ConcurrentLinkedDeque;import java.util.Deque;public class Example { public static void main(String[] args) { Deque<Integer> deque = new ConcurrentLinkedDeque<>(); deque.addFirst(1); deque.addLast(2); int first = deque.pollFirst(); int last = deque.pollLast(); System.out.println("First: " + first + ", Last: " + last); }} |
Output
First: 1, Last: 2
Advantages of using ConcurrentLinkedDeque:
- Thread-safe: The ConcurrentLinkedDeque class is thread-safe, which means that multiple threads can access it simultaneously without encountering data corruption.
- Efficient: The ConcurrentLinkedDeque class provides constant-time performance for inserting and removing elements from both ends of the deque, making it a good choice for scenarios where you need to perform many add and remove operations.
- Scalable: The ConcurrentLinkedDeque class uses a linked list to store its elements, which makes it scalable and suitable for use in high-performance and concurrent applications.
- High-concurrency: The ConcurrentLinkedDeque class uses lock-free algorithms, which means that multiple threads can access the deque simultaneously without locking, making it suitable for high-concurrency applications.
Disadvantages of using ConcurrentLinkedDeque:
- More memory overhead: The ConcurrentLinkedDeque class uses a linked list to store its elements, which means that it requires more memory overhead than an array-based implementation, such as the ArrayDeque class.
- Limited capacity: The ConcurrentLinkedDeque class does not have a limited capacity, but it still requires memory for storing its elements, which means that you may need to create a new ConcurrentLinkedDeque when the old one consumes too much memory.
Class Hierarchy:
Declaration:
public abstract class ConcurrentLinkedDeque<E>
extends AbstractCollection<E>
implements Deque<E>, Serializable
Here, E is the type of elements maintained by this collection.
It implements Serializable, Iterable<E>, Collection<E>, Deque<E>, Queue<E> interfaces.
Constructors of ConcurrentLinkedDeque:
1. ConcurrentLinkedDeque(): This constructor is used to construct an empty deque.
ConcurrentLinkedDeque<E> cld = new ConcurrentLinkedDeque<E>();
2. ConcurrentLinkedDeque(Collection<E> c): This constructor is used to construct a deque with the elements of the Collection passed as the parameter.
ConcurrentLinkedDeque<E> cld = new ConcurrentLinkedDeque<E>(Collection<E> c);
Below is the sample program to illustrate ConcurrentLinkedDeque in Java:
Java
// Java Program to demonstrate ConcurrentLinkedDequeimport java.util.concurrent.*;class ConcurrentLinkedDequeDemo { public static void main(String[] args) { // Create a ConcurrentLinkedDeque // using ConcurrentLinkedDeque() // constructor ConcurrentLinkedDeque<Integer> cld = new ConcurrentLinkedDeque<Integer>(); // add element to the front // using addFirst() method cld.addFirst(12); cld.addFirst(70); cld.addFirst(1009); cld.addFirst(475); // Displaying the existing ConcurrentLinkedDeque System.out.println("ConcurrentLinkedDeque: " + cld); // Create a ConcurrentLinkedDeque // using ConcurrentLinkedDeque(Collection c) // constructor ConcurrentLinkedDeque<Integer> cld1 = new ConcurrentLinkedDeque<Integer>(cld); // Displaying the existing ConcurrentLinkedDeque System.out.println("ConcurrentLinkedDeque1: " + cld1); }} |
Output
ConcurrentLinkedDeque: [475, 1009, 70, 12] ConcurrentLinkedDeque1: [475, 1009, 70, 12]
Example:
Java
// Java code to illustrate// methods of ConcurrentLinkedDequeimport java.util.concurrent.*;class ConcurrentLinkedDequeDemo { public static void main(String[] args) { // Create a ConcurrentLinkedDeque // using ConcurrentLinkedDeque() constructor ConcurrentLinkedDeque<Integer> cld = new ConcurrentLinkedDeque<Integer>(); // add element to the front // using addFirst() method cld.addFirst(12); cld.addFirst(70); cld.addFirst(1009); cld.addFirst(475); // Displaying the existing ConcurrentLinkedDeque System.out.println("ConcurrentLinkedDeque: " + cld); // Displaying the Last element // using getLast() method System.out.println("The Last element is: " + cld.getLast()); // Displaying the first element // using peekFirst() method System.out.println("First Element is: " + cld.peekFirst()); // Remove the Last element // using removeLast() method cld.removeLast(); // Displaying the existing ConcurrentLinkedDeque System.out.println("ConcurrentLinkedDeque: " + cld); }} |
Output
ConcurrentLinkedDeque: [475, 1009, 70, 12] The Last element is: 12 First Element is: 475 ConcurrentLinkedDeque: [475, 1009, 70]
Basic Operations of ConcurrentLinkedDeque
1. Adding Elements
To add an element or Collection of elements, ConcurrentLinkedDeque provides methods like add(E e), addAll(Collection<? extends E> c), addFirst(E e), addLast(E e) methods. The example below explains these methods.
Java
// Java Program Demonstrate adding// elements to the ConcurrentLinkedDequeimport java.util.concurrent.*;class AddingElements { public static void main(String[] args) { // create instance using ConcurrentLinkedDeque ConcurrentLinkedDeque<Integer> cld1 = new ConcurrentLinkedDeque<Integer>(); // Add element to the tail using // add or addLast methods cld1.add(12); cld1.add(110); // Add element to the head // using addFirst method cld1.addFirst(55); // Displaying the existing ConcurrentLinkedDeque System.out.println("Initial Elements in " + "the LinkedDeque cld : " + cld1); // create instance using ConcurrentLinkedDeque ConcurrentLinkedDeque<Integer> cld2 = new ConcurrentLinkedDeque<Integer>(); // Add elements of cld1 to the // cld2 using addAll method cld2.addAll(cld1); // Displaying the modified ConcurrentLinkedDeque System.out.println("Initial Elements in " + "the LinkedDeque cld2: " + cld2); }} |
Output
Initial Elements in the LinkedDeque cld : [55, 12, 110] Initial Elements in the LinkedDeque cld2: [55, 12, 110]
Output:
Initial Elements in the LinkedDeque cld : [55, 12, 110] Initial Elements in the LinkedDeque cld2: [55, 12, 110]
2. Remove Elements
To remove an element, ConcurrentLinkedDeque provides methods like remove(), remove(Object o), removeFirst(), removeLast() etc. These methods are explained in the below example.
Java
// Java Program to demonstrate removing// elements of ConcurrentLinkedDequeimport java.util.concurrent.*;class RemovingElements { public static void main(String[] args) { // Create a ConcurrentLinkedDeque // using ConcurrentLinkedDeque() constructor ConcurrentLinkedDeque<Integer> cld = new ConcurrentLinkedDeque<Integer>(); // Add elements using add() method cld.add(40); cld.add(50); cld.add(60); cld.add(70); cld.add(80); // Displaying the existing LinkedDeque System.out.println( "Existing ConcurrentLinkedDeque: " + cld); // remove method removes the first // element of ConcurrentLinkedDeque // using remove() method System.out.println("Element removed: " + cld.remove()); // Remove 60 using remove(Object) System.out.println("60 removed: " + cld.remove(60)); // Displaying the existing ConcurrentLinkedDeque System.out.println( "Modified ConcurrentLinkedDeque: " + cld); // Remove the first element cld.removeFirst(); // Remove the Last element cld.removeLast(); // Displaying the existing ConcurrentLinkedDeque System.out.println( "Modified ConcurrentLinkedDeque: " + cld); }} |
Output
Existing ConcurrentLinkedDeque: [40, 50, 60, 70, 80] Element removed: 40 60 removed: true Modified ConcurrentLinkedDeque: [50, 70, 80] Modified ConcurrentLinkedDeque: [70]
3. Iterating Elements
We can iterate the ConcurrentLinkedDeque using iterator() or descendingIterator() methods. The below code explains both these methods.
Java
// Java code to illustrate iterating// elements of ConcurrentLinkedDequeimport java.util.concurrent.*;import java.util.*;public class IteratingConcurrentLinkedDeque { public static void main(String args[]) { // Creating an empty ConcurrentLinkedDeque ConcurrentLinkedDeque<String> deque = new ConcurrentLinkedDeque<String>(); // Use add() method to add elements // into the ConcurrentLinkedDeque deque.add("Welcome"); deque.add("To"); deque.add("Geeks"); deque.add("4"); deque.add("Geeks"); // Displaying the ConcurrentLinkedDeque System.out.println("ConcurrentLinkedDeque: " + deque); // Creating an iterator Iterator fitr = deque.iterator(); // Displaying the values // after iterating through the ConcurrentLinkedDeque System.out.println("The iterator values are: "); while (fitr.hasNext()) { System.out.println(fitr.next()); } // Creating a desc_iterator Iterator ditr = deque.descendingIterator(); // Displaying the values after iterating // through the ConcurrentLinkedDeque // in reverse order System.out.println("The iterator values are: "); while (ditr.hasNext()) { System.out.println(ditr.next()); } }} |
Output
ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks] The iterator values are: Welcome To Geeks 4 Geeks The iterator values are: Geeks 4 Geeks To Welcome
4. Accessing Elements
To access the elements of ConcurrentLinkedDeque, it provides methods like getFirst(), getLast(), element() methods. The below example explains these methods.
Java
// Java Program to Demonstrate accessing// elements of ConcurrentLinkedDequeimport java.util.concurrent.*;import java.util.*;class Accessing { public static void main(String[] args) { // Creating an empty ConcurrentLinkedDeque ConcurrentLinkedDeque<String> cld = new ConcurrentLinkedDeque<String>(); // Add elements into the ConcurrentLinkedDeque cld.add("Welcome"); cld.add("To"); cld.add("Geeks"); cld.add("4"); cld.add("Geeks"); // Displaying the ConcurrentLinkedDeque System.out.println("Elements in the ConcurrentLinkedDeque: " + cld); // Displaying the first element System.out.println("The first element is: " + cld.getFirst()); // Displaying the Last element System.out.println("The Last element is: " + cld.getLast()); // Displaying the head of ConcurrentLinkedDeque System.out.println("The Head of ConcurrentLinkedDeque is: " + cld.element()); }} |
Output
Elements in the ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks] The first element is: Welcome The Last element is: Geeks The Head of ConcurrentLinkedDeque is: Welcome
Output:
Elements in the ConcurrentLinkedDeque: [Welcome, To, Geeks, 4, Geeks] The first element is: Welcome The Last element is: Geeks The Head of ConcurrentLinkedDeque is: Welcome
Methods of ConcurrentLinkedDeque
Here, E is the type of element.
|
METHOD |
DESCRIPTION |
|---|---|
| add(E e) | Inserts the specified element at the tail of this deque. |
| addAll(Collection<? extends E> c) | Appends all of the elements in the specified collection to the end of this deque, in the order that they are returned by the specified collection’s iterator. |
| addFirst(E e) | Inserts the specified element at the front of this deque. |
| addLast(E e) | Inserts the specified element at the end of this deque. |
| clear() | Removes all of the elements from this deque. |
| contains(Object o) | Returns true if this deque contains the specified element. |
| descendingIterator() | Returns an iterator over the elements in this deque in reverse sequential order. |
| element() | Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this 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() | Retrieves, but does not remove, the first element of this deque. |
| getLast() | Retrieves, but does not remove, the last element of this deque. |
| isEmpty() | Returns true if this collection contains no elements. |
| iterator() | Returns an iterator over the elements in this deque in the proper sequence. |
| offer(E e) | Inserts the specified element at the tail of this deque. |
| offerFirst(E e) | Inserts the specified element at the front of this deque. |
| offerLast(E e) | Inserts the specified element at the end of this deque. |
| pop() | Pops an element from the stack represented by this deque. |
| push(E e) | Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available. |
| remove() | Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). |
| remove(Object o) | Removes the first occurrence 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() | Retrieves and removes the first element of this deque. |
| removeFirstOccurrence(Object o) | Removes the first occurrence of the specified element from this deque. |
| removeIf(Predicate<? super E> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
| removeLast() | Retrieves and removes the last element of this deque. |
| removeLastOccurrence(Object o) | Removes the last occurrence of the specified element from this deque. |
| 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() | Returns a 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 last element). |
| toArray(T[] a) | Returns an array containing all of the elements in this deque, in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. |
Methods declared in class java.util.AbstractCollection
|
METHOD |
DESCRIPTION |
|---|---|
| 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 declared in interface java.util.Collection
|
METHOD |
DESCRIPTION |
|---|---|
| containsAll(Collection<?> c) | Returns true if this collection contains all of the elements in the specified collection. |
| equals(Object o) | 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 |
DESCRIPTION |
|---|---|
| peek() | Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty. |
| 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. |
| poll() | Retrieves and removes the head of the queue represented by this deque (in other words, the first 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. |
Reference Book:
“Java Concurrency in Practice” by Brian Goetz, Tim Peierls, Joshua Bloch, Joseph Bowbeer, David Holmes, and Doug Lea is a comprehensive guide to concurrent programming in Java, including the ConcurrentLinkedDeque class. This book covers the basics of concurrent programming, explains how to use the java.util.concurrent package, and provides tips and best practices for writing correct and efficient code. If you’re looking to learn more about the ConcurrentLinkedDeque class and concurrent programming in general, this book is an excellent resource.
