PriorityQueue: A queue that retrieves elements based on priority.
Example:

import java.util.PriorityQueue;
PriorityQueue pq = new PriorityQueue<>();
pq.add(30);
pq.add(10);
pq.add(20);
System.out.println(pq);
System.out.println("Poll: " + pq.poll());
System.out.println(pq);