ArrayBlockingQueue Class in Java
Last Updated :
11 Jul, 2025
In Java, the ArrayBlockingQueue class is part of the java.util.concurrent package and implements the BlockingQueue interface. It is a thread-safe, bounded queue that helps manage producer-consumer scenarios by blocking threads when the queue is full or empty.
- The queue has a fixed size, specified during creation.
- Methods like take() and put() block the calling thread when the queue is full or empty
- It is safe for use in multi-threaded environments without needing additional synchronization.
Example: This example demonstrates how to use ArrayBlockingQueue with a fixed capacity, blocking if the queue is full.
Java
// Java Program to demonstrates
// the working of ArrayBlockingQueue
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks {
public static void main(String[] args)
throws InterruptedException
{
// Create an ArrayBlockingQueue
// with a capacity of 3
ArrayBlockingQueue<Integer> q
= new ArrayBlockingQueue<>(3);
// Adding elements to the queue
q.put(1);
q.put(2);
q.put(3);
// Print the queue after adding elements
System.out.println("Queue after adding elements: "
+ q);
}
}
OutputQueue after adding elements: [1, 2, 3]
ArrayBlockingQueue Hierarchy
The below diagram demonstrates the class hierarchy for ArrayBlockingQueue and LinkedListBlockingQueue, both implementing the BlockingQueue interface, which extends Queue, Collection, and Iterable
Declaration of ArrayBlockingQueue
In Java, the declaration of ArrayBlockingQueue can be done as:
ArrayBlockingQueue<Type> queue = new ArrayBlockingQueue<>(capacity)
Note: Here Type is the type of element the queue will hold (e.g Integer, String) and capacity is the maximum number of elements the queue can hold.
Constructors
Constructor | Description |
|---|
ArrayBlockingQueue(int capacity) | Creates an ArrayBlockingQueue with the given (fixed) capacity and default access policy. |
ArrayBlockingQueue(int capacity, boolean fair) | reates a queue with the specified capacity and a fair or non-fair locking policy based on the fair argument. |
ArrayBlockingQueue(int capacity, boolean fair, Collection c) | Creates a queue with the specified capacity, locking policy, and initializes it with elements from the given collection |
Example: This example demonstrates the creation of an ArrayBlockingQueue with a specified capacity and adding elements to it.
Java
// Java program to demonstrate the working of
// ArrayBlockingQueue(int initialCapacity)
// constructor
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks {
public static void main(String[] args)
{
// define capacity of ArrayBlockingQueue
int c = 15;
// create object of ArrayBlockingQueue
// using ArrayBlockingQueue(int initialCapacity) constructor
ArrayBlockingQueue<Integer> a = new ArrayBlockingQueue<Integer>(c);
// add numbers
a.add(1);
a.add(2);
a.add(3);
// print queue
System.out.println("ArrayBlockingQueue:" + a);
}
}
OutputArrayBlockingQueue:[1, 2, 3]
Performing Various Operations on ArrayBlockingQueue
1. Adding Elements: We use add() method to insert elements into an ArrayBlockingQueue.
Example: This example demonstrates how to create and add elements to an ArrayBlockingQueue.
Java
// Adding elements to an ArrayBlockingQueue
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks {
public static void main(String[] args)
{
// define capacity of ArrayBlockingQueue
int c = 15;
// create object of ArrayBlockingQueue
ArrayBlockingQueue<Integer> a
= new ArrayBlockingQueue<Integer>(c);
// add numbers
a.add(100);
a.add(200);
a.add(300);
// print queue
System.out.println("ArrayBlockingQueue : " + a);
}
}
OutputArrayBlockingQueue : [100, 200, 300]
2. Removing Elements: We can use remove() method to remove elements from the ArrayBlockingQueue.
Example: This example demonstrates how to remove a specific element from an ArrayBlockingQueue.
Java
// Remove elements from an ArrayBlockingQueue
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks{
public static void main(String[] args)
{
// define capacity of ArrayBlockingQueue
int c = 15;
// create object of ArrayBlockingQueue
ArrayBlockingQueue<Integer> a = new ArrayBlockingQueue<Integer>(c);
// add numbers
a.add(1);
a.add(2);
a.add(3);
// print queue
System.out.println("ArrayBlockingQueue: " + a);
// remove 223
boolean b = a.remove(2);
// print Queue
System.out.println("Element 2 removed ?: " + b);
// print Queue
System.out.println("Updated ArrayBlockingQueue: " + a);
}
}
OutputArrayBlockingQueue: [1, 2, 3]
Element 2 removed ?: true
Updated ArrayBlockingQueue: [1, 3]
3. Accessing Elements: We can use the peek() method to retrieve the head of the queue without removing it.
Example: This example demonstrates how to retrieve the head of the queue using the peek() method.
Java
// Accessing elements in an ArrayBlockingQueue
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks{
public static void main(String[] args)
{
// Define capacity of ArrayBlockingQueue
int c = 5;
// Create object of ArrayBlockingQueue
ArrayBlockingQueue<Integer> q = new ArrayBlockingQueue<Integer>(c);
// Add element to ArrayBlockingQueue
q.add(23);
q.add(32);
q.add(45);
q.add(12);
// Print queue
System.out.println("ArrayBlockingQueue is: " + q);
// Print head of queue using peek() method
System.out.println("Head of queue is: " + q.peek());
}
}
OutputArrayBlockingQueue is: [23, 32, 45, 12]
Head of queue is: 23
4. Iterating Elements: We use iterator() method to iterate over the elements of an ArrayBlockingQueue in the order from head to tail.
Example: This example demonstrates how to use the iterator() method to iterate over the elements of an ArrayBlockingQueue.
Java
// Iterating elements in an ArrayBlockingQueue
import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;
public class Geeks {
public static void main(String[] args)
{
// Define capacity of ArrayBlockingQueue
int c = 5;
// Create object of ArrayBlockingQueue
ArrayBlockingQueue<String> q
= new ArrayBlockingQueue<String>(c);
// Add elements to ArrayBlockingQueue
q.offer("Java");
q.offer("C++");
q.offer("Python");
q.offer("Js");
// Print ArrayBlockingQueue
System.out.println("ArrayBlockingQueue is: " + q);
// Call iterator() method and Create an iterator
Iterator i = q.iterator();
// Print elements of iterator
System.out.println("The iterator values:");
while (i.hasNext()) {
System.out.print(i.next() + " ");
}
}
}
OutputArrayBlockingQueue is: [Java, C++, Python, Js]
The iterator values:
Java C++ Python Js
Methods
Methods | Description |
|---|
| add(E e) | Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and throwing an IllegalStateException if this queue is full. |
| clear() | Atomically removes all of the elements from this queue. |
| contains(Object o) | Returns true if this queue contains the specified element. |
| drainTo(Collection<? super E> c) | Removes all available elements from this queue and adds them to the given collection. |
| drainTo(Collection<? super E> c, int maxElements) | Removes at most the given number of available elements from this queue and adds them to the given collection. |
| 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. |
| iterator() | Returns an iterator over the elements in this queue in the proper sequence. |
| offer(E e) | Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full. |
| offer(E e, long timeout, TimeUnit unit) | Inserts the specified element at the tail of this queue, waiting up to the specified wait time for space to become available if the queue is full. |
| put(E e) | Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full. |
| remainingCapacity() | Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking. |
| remove(Object o) | Removes a single instance of the specified element from this queue, if it is present. |
| removeAll(Collection<?> c) | Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
| removeIf(Predicate<? super E> filter) | Removes all of the elements of this collection that satisfy the given predicate. |
| 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 queue. |
| spliterator() | Returns a Spliterator over the elements in this queue. |
| toArray() | Returns an array containing all of the elements in this queue, in proper sequence. |
| toArray(T[] a) | Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array. |
Methods Declared in Class java.util.AbstractQueue
Methods Declared in Class java.util.AbstractCollection
Methods | Description |
|---|
| containsAll(Collection<?> c) | Returns true if this collection contains all of the elements in the specified collection. |
| isEmpty() | Returns true if this collection contains no elements. |
| toString() | Returns a string representation of this collection. |
Methods Declared in Interface java.util.concurrent.BlockingQueue
Methods | Description |
|---|
| poll(long timeout, TimeUnit unit) | Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available. |
| take() | Retrieves and removes the head of this queue, waiting if necessary until an element becomes available. |
Methods Declared in Interface java.util.Collection
Methods | Description |
|---|
| addAll(Collection<? extends E> c) | Adds all of the elements in the specified collection to this collection (optional operation). |
| 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. |
| isEmpty() | Returns true if this collection contains no elements. |
| 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.Queue
Methods | Description |
|---|
| element() | Retrieves, but does not remove, the head of this queue. |
| peek() | Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. |
| poll() | Retrieves and removes the head of this queue, or returns null if this queue is empty. |
| remove() | Retrieves and removes the head of this queue. |
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