Java : Priority Queue

Question

I have a java program which goes like this

public class PriorityQueueExample {

public static void main(String[] args) {
    PriorityQueue

        

Answer 1

Insertion into a priority queue is not enough to sort a list of elements, since it doesn't store them in sorted order; it stores them in the partially sorted heap order. You have to remove the elements in a loop to sort them:

while (pq.size() > 0)
    System.out.println(pq.remove());

Answer 2

poll() and remove() will give sorted order not peek() as per java8.

 PriorityQueue<Integer> pq = new PriorityQueue<Integer>();
    pq.add(10);
    pq.add(1);
    pq.add(9);
    pq.add(2);
    pq.add(8);
    pq.add(3);
    pq.add(7);
    pq.add(4);
    pq.add(6);
    pq.add(5);
        // Remove items from the Priority Queue (DEQUEUE)
        while (!pq.isEmpty()) {
          //  System.out.println(pq.remove());
          System.out.println(pq.poll());
        }
Output for poll() & remove():
1 
2
3 
4 
5 
6 
7 
8 
9 
10
output for peek():
1
1
1
1
1
1
1
1
1
1

Answer 3

It is sorted, but internally the elements are stored in a heap. If you call peek(), poll(), or remove(), you will get the right order (and that's how you access queues).