PriorityBlockingQueue is an unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. The “blocking” part of the name is added to imply the thread will block waiting until there’s an item available on the queue. This class does not permit null elements. A priority queue relying on natural ordering also does not permit the insertion of non-comparable objects (doing so results in ClassCastException).
It implements Serializable, Iterable<E>, Collection<E>, BlockingQueue<E>, Queue<E> interfaces and extends AbstractQueue<E> class.
Declaration:
public class PriorityBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable // Here, E is the type of elements held in this collection
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.PriorityBlockingQueue<E>
Implementation:
Example
Java
// Java Program to Implement PriorityBlockingQueue API// Importing concurrent classes from// java.util packageimport java.util.concurrent.PriorityBlockingQueue;import java.util.concurrent.TimeUnit;// Class for PriorityQueuepublic class GFG { // Main driver method public static void main(String[] args) throws InterruptedException { // Creating a new object of PriorityBlockingQueue // Declaring Integer type object PriorityBlockingQueue<Integer> priorityBlockingQueue = new PriorityBlockingQueue<>(); // Creation of a thread new Thread(() -> { // Display message System.out.println("Waiting to poll ..."); // Try block to check for exceptions try { // Condition check while (true) { // Return (integer) value at head of // queue of PriorityBlockingQueue Integer poll = priorityBlockingQueue.take(); // Display and print element returned in // PriorityBlockingQueue System.out.println("Polled : " + poll); // Pause the execution of current thread // for certain amount of time using // toMills() method() to showcase // working of PriorityBlockingQueue Thread.sleep( TimeUnit.SECONDS.toMillis(1)); } } // Catch block to handle exceptions if any catch (InterruptedException e) { // Print and display the line number // where exception/s occurred e.printStackTrace(); } // Execution of thread begins with // use of start() method }).start(); // Custom elements inputs // 1, 2, 3 to priorityBlockingQueue // Pausing execution of first thread Thread.sleep(TimeUnit.SECONDS.toMillis(2)); // Insert parameter element-> 1 to method // at the tail of priority queue priorityBlockingQueue.add(1); // Pausing execution of second thread Thread.sleep(TimeUnit.SECONDS.toMillis(2)); // Insert parameter element-> 2 to method // at the tail of priority queue priorityBlockingQueue.add(2); // pausing execution of third thread Thread.sleep(TimeUnit.SECONDS.toMillis(2)); // Insert parameter element-> 3 to method // at the tail of priority queue priorityBlockingQueue.add(3); }} |
Output:
