What is the output?

import java.util.*;
public class Main {
    public static void main(String[] args)
    {
        PriorityQueue<Integer> queue = new PriorityQueue<>();
        queue.add(4);
        queue.add(3);
        queue.add(2);
        queue.add(1);
        while (queue.isEmpty() == false) {
            System.out.printf("%d", queue.remove());
        }
    }
}