PriorityQueue<Integer> pQueue = new PriorityQueue<Integer>();
This line creates a priority queue of Integers. A priority queue stores a “sorted” list of items (in your case Integers).
When you add an int to pQueue ,it is places the value in the correct position.
E.g if I add numbers 1, 10 and 5 in this order to a priority Queue, something like this will happen:
pqueue = {} //empty at start
pqueue = {1} //1 added
pqueue = {1->10} //10 added
pqueue = {1->5->10} // 5 added
notice how 5 gets placed between 1 and 10.
When you call pQueue.poll(); the first element of pQueue is returned which is guaranteed to be the smallest value inside the queue. (The value is removed from the queue during this process).
Repeated calls would return the numbers in the example above in the order 1 , 5, 10.
Due to this your array gets sorted.
solved Heap Sort array