The ArrayBlockingQueue
class of the Java Collections framework provides the blocking queue implementation using an array.
It implements the Java BlockingQueue interface.
Creating ArrayBlockingQueue
In order to create an array blocking queue, we must import the java.util.concurrent.ArrayBlockingQueue
package.
Once we import the package, here is how we can create an array blocking queue in Java:
ArrayBlockingQueue<Type> animal = new ArrayBlockingQueue<>(int capacity);
Here,
- Type - the type of the array blocking queue
- capacity - the size of the array blocking queue
For example,
// Creating String type ArrayBlockingQueue with size 5
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
// Creating Integer type ArrayBlockingQueue with size 5
ArrayBlockingQueue<Integer> age = new ArrayBlockingQueue<>(5);
Note: It is compulsory to provide the size of the array.
Methods of ArrayBlockingQueue
The ArrayBlockingQueue
class provides the implementation of all the methods in the BlockingQueue
interface.
These methods are used to insert, access and delete elements from array blocking queues.
Also, we will learn about two methods put()
and take()
that support the blocking operation in the array blocking queue.
These two methods distinguish the array blocking queue from other typical queues.
Insert Elements
add()
- Inserts the specified element to the array blocking queue. It throws an exception if the queue is full.offer()
- Inserts the specified element to the array blocking queue. It returnsfalse
if the queue is full.
For example,
import java.util.concurrent.ArrayBlockingQueue;
class Main {
public static void main(String[] args) {
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
// Using add()
animals.add("Dog");
animals.add("Cat");
// Using offer()
animals.offer("Horse");
System.out.println("ArrayBlockingQueue: " + animals);
}
}
Output
ArrayBlockingQueue: [Dog, Cat, Horse]
Access Elements
peek()
- Returns an element from the front of the array blocking queue. It returnsnull
if the queue is empty.iterator()
- Returns an iterator object to sequentially access elements from the array blocking queue. It throws an exception if the queue is empty. We must import thejava.util.Iterator
package to use it.
For example,
import java.util.concurrent.ArrayBlockingQueue;
import java.util.Iterator;
class Main {
public static void main(String[] args) {
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
// Add elements
animals.add("Dog");
animals.add("Cat");
animals.add("Horse");
System.out.println("ArrayBlockingQueue: " + animals);
// Using peek()
String element = animals.peek();
System.out.println("Accessed Element: " + element);
// Using iterator()
Iterator<String> iterate = animals.iterator();
System.out.print("ArrayBlockingQueue Elements: ");
while(iterate.hasNext()) {
System.out.print(iterate.next());
System.out.print(", ");
}
}
}
Output
ArrayBlockingQueue: [Dog, Cat, Horse] Accessed Element: Dog ArrayBlockingQueue Elements: Dog, Cat, Horse,
Remove Elements
remove()
- Returns and removes a specified element from the array blocking queue. It throws an exception if the queue is empty.poll()
- Returns and removes a specified element from the array blocking queue. It returnsnull
if the queue is empty.clear()
- Removes all the elements from the array blocking queue.
For example,
import java.util.concurrent.ArrayBlockingQueue;
class Main {
public static void main(String[] args) {
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
animals.add("Dog");
animals.add("Cat");
animals.add("Horse");
System.out.println("ArrayBlockingQueue: " + animals);
// Using remove()
String element1 = animals.remove();
System.out.println("Removed Element:");
System.out.println("Using remove(): " + element1);
// Using poll()
String element2 = animals.poll();
System.out.println("Using poll(): " + element2);
// Using clear()
animals.clear();
System.out.println("Updated ArrayBlockingQueue: " + animals);
}
}
Output
ArrayBlockingQueue: [Dog, Cat, Horse] Removed Elements: Using remove(): Dog Using poll(): Cat Updated ArrayBlockingQueue: []
put() and take() Method
In multithreading processes, we can use put()
and take()
to block the operation of one thread to synchronize it with another thread. These methods will wait until they can be successfully executed.
put() method
To add an element to the end of an array blocking queue, we can use the put()
method.
If the array blocking queue is full, it waits until there is space in the array blocking queue to add an element.
For example,
import java.util.concurrent.ArrayBlockingQueue;
class Main {
public static void main(String[] args) {
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
try {
// Add elements to animals
animals.put("Dog");
animals.put("Cat");
System.out.println("ArrayBlockingQueue: " + animals);
}
catch(Exception e) {
System.out.println(e);
}
}
}
Output
ArrayBlockingQueue: [Dog, Cat]
Here, the put()
method may throw an InterruptedException
if it is interrupted while waiting. Hence, we must enclose it inside a try..catch block.
take() Method
To return and remove an element from the front of the array blocking queue, we can use the take()
method.
If the array blocking queue is empty, it waits until there are elements in the array blocking queue to be deleted.
For example,
import java.util.concurrent.ArrayBlockingQueue;
class Main {
public static void main(String[] args) {
ArrayBlockingQueue<String> animals = new ArrayBlockingQueue<>(5);
try {
//Add elements to animals
animals.put("Dog");
animals.put("Cat");
System.out.println("ArrayBlockingQueue: " + animals);
// Remove an element
String element = animals.take();
System.out.println("Removed Element: " + element);
}
catch(Exception e) {
System.out.println(e);
}
}
}
Output
ArrayBlockingQueue: [Dog, Cat] Removed Element: Dog
Here, the take()
method will throw an InterrupedException
if it is interrupted while waiting. Hence, we must enclose it inside a try...catch
block.
Other Methods
Methods | Descriptions |
---|---|
contains(element) |
Searches the array blocking queue for the specified element.If the element is found, it returns true , if not it returns false . |
size() |
Returns the length of the array blocking queue. |
toArray() |
Converts array blocking queue to an array and returns it. |
toString() |
Converts the array blocking queue to string |
Why use ArrayBlockingQueue?
The ArrayBlockingQueue
uses arrays as its internal storage.
It is considered as a thread-safe collection. Hence, it is generally used in multi-threading applications.
Suppose, one thread is inserting elements to the queue and another thread is removing elements from the queue.
Now, if the first thread is slower than the second thread, then the array blocking queue can make the second thread waits until the first thread completes its operations.