How to Implement BlockingQueue Interface in Java

A queue is an important aspect of any Programming language. Especially if we talk about Java. In this article, we will discuss the BlockingQueue Interface in Java in the following order:

• What is a BlockingQueue Interface in Java?
• BlockingQueue Types
• Methods in BlockingQueue Interface
• BlockingQueue Interface in Java Example: Service

What is a BlockingQueue Interface in Java?

A BlockingQueue Interface in Java is a queue that blocks when you try to dequeue from it and the queue is empty, or if you try to enqueue items to it and the queue is already full. A thread trying to dequeue from an empty queue is blocked until some other thread inserts an item into the queue. A thread trying to enqueue an item in a full queue is blocked until some other thread makes space in the queue, either by dequeuing one or more items or clearing the queue completely.

BlockingQueue Interface in Java doesn’t accept null values and throw NullPointerException if you try to store the null value in the queue. Java BlockingQueue implementations are thread-safe. All queuing methods are atomic in nature and use internal locks or other forms of concurrency control.

Java Queue Class Diagram

Java Queue interface extends the Collection interface. The Collection interface extends the Iterable interface. Some of the frequently used Queue implementation classes are LinkedList, PriorityQueue, ArrayBlockingQueue, DelayQueue, LinkedBlockingQueue, PriorityBlockingQueue, etc.. AbstractQueue provides a skeletal implementation of the Queue interface to reduce the effort in implementing Queue.

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BlockingQueue Types

The BlockingQueue are two types:

• Unbounded Queue: The Capacity of the blocking queue will be set to Integer.MAX_VALUE. In the case of unbounded blocking queue, queue will never block because it could grow to a very large size. when you add elements it’s size grow.

Syntax:
BlockingQueue blocking queue = new LinkedBlockingDeque();

• Bounded Queue: The second type of queue is the bounded queue. In case of the bounded queue you can create a queue bypassing the capacity of the queue in queues constructor:
  Syntax:
  // Creates a Blocking Queue with capacity 5

BlockingQueue blocking queue = new LinkedBlockingDeque(5);

Methods in BlockingQueue Interface

BlockingQueue Interface in Java Example: Service

package com.journaldev.concurrency;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.BlockingQueue;

public class ProducerConsumerService {

    public static void main(String[] args) {

        //Creating BlockingQueue of size 10

        BlockingQueue<Message> queue = new ArrayBlockingQueue<>(10);

        Producer producer = new Producer(queue);	

        Consumer consumer = new Consumer(queue);

        //starting producer to produce messages in queue

        new Thread(producer).start();

        //starting consumer to consume messages from queue

        new Thread(consumer).start();

        System.out.println("Producer and Consumer has been started");

    }

}

With this, we come to an end of the BlockingQueue Interface in Java article. I hope all your concepts are now clear.

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