Java PriorityBlockingQueue

Java PriorityBlockingQueue is a concurrent collection and an implementation of BlockingQueue. PriorityBlockingQueue is an unbounded collection. Ordering of elements in the PriorityBlockingQueue is done same as in PriorityQueue.

We should see PriorityBlockingQueue as a PriorityQueue with added operations for blocking retrieval. All the rules of PriorityQueue applies here like elements are ordered based on their priority level among the elements.

PriorityBlockingQueue Example

Let us have a look at a producer-consumer based example to understand the PriorityBlockingQueue.

PriorityBlockingQueueProducer.java

package com.javapapers.java.collections;

import java.util.Random;
import java.util.UUID;
import java.util.concurrent.BlockingQueue;

public class PriorityBlockingQueueProducer implements Runnable {

	protected BlockingQueue<String> blockingQueue;
	final Random random = new Random();

	public PriorityBlockingQueueProducer(BlockingQueue<String> queue) {
		this.blockingQueue = queue;
	}

	@Override
	public void run() {
		while (true) {
			try {
				String data = UUID.randomUUID().toString();
				System.out.println("Put: " + data);
				blockingQueue.put(data);
				Thread.sleep(500);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}

PriorityBlockingQueueConsumer.java

package com.javapapers.java.collections;

import java.util.concurrent.BlockingQueue;

public class PriorityBlockingQueueConsumer implements Runnable {

	protected BlockingQueue<String> blockingQueue;

	public PriorityBlockingQueueConsumer(BlockingQueue<String> queue) {
		this.blockingQueue = queue;
	}

	@Override
	public void run() {
		while (true) {
			try {
				String data = blockingQueue.take();
				System.out.println(Thread.currentThread().getName()
						+ " take(): " + data);
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}

PriorityBlockingQueueExample.java

package com.javapapers.java.collections;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

public class PriorityBlockingQueueExample {
	public static void main(String[] args) {
		final BlockingQueue<String> priorityBlockingQueue = new LinkedBlockingQueue<String>();

		PriorityBlockingQueueProducer queueProducer = new PriorityBlockingQueueProducer(
				priorityBlockingQueue);
		new Thread(queueProducer).start();

		PriorityBlockingQueueConsumer queueConsumer1 = new PriorityBlockingQueueConsumer(
				priorityBlockingQueue);
		new Thread(queueConsumer1).start();

		PriorityBlockingQueueConsumer queueConsumer2 = new PriorityBlockingQueueConsumer(
				priorityBlockingQueue);
		new Thread(queueConsumer2).start();

	}
}

PriorityBlockingQueue Example Output

Put: ebc55884-84d7-4621-b3d7-2e7c9c428a13
Thread-1 take(): ebc55884-84d7-4621-b3d7-2e7c9c428a13
Put: 1f8e4b4e-03df-4068-a2e1-423f1f6091a1
Thread-2 take(): 1f8e4b4e-03df-4068-a2e1-423f1f6091a1
Put: 55a38169-24a1-459b-ad1a-51b0ba36a7b8
Thread-1 take(): 55a38169-24a1-459b-ad1a-51b0ba36a7b8
Put: 84af8597-2796-4050-8c19-711d68f8ce6b
Thread-2 take(): 84af8597-2796-4050-8c19-711d68f8ce6b
Put: 3cb2bcae-8a71-4d75-96bb-72549ffd6283
Thread-1 take(): 3cb2bcae-8a71-4d75-96bb-72549ffd6283