ADDITIONAL SYSTEM INFORMATION :
Linux Mint 19.1 64bit
openjdk 11.0.3 2019-04-16
OpenJDK Runtime Environment (build 11.0.3+7-Ubuntu-1ubuntu218.04.1)
OpenJDK 64-Bit Server VM (build 11.0.3+7-Ubuntu-1ubuntu218.04.1, mixed mode, sharing)


A DESCRIPTION OF THE PROBLEM :
I created an instance of PriorityQueue using the constructor accepting an Comparator instance (created with help of Comparator.comparingInt method). Then I added elements with decreasing int value that is used by aforementioned comparingInt.

In cases, where queue has exactly 3 elements, the order returned by iterator is incorrect. Strangely enough, when elements are added in ascending order, returned sequence is actually correct. For queues of 4 elements (or bigger) it seems, like order is always correct.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the code below

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
1
2
3
ACTUAL -
3
2
1

---------- BEGIN SOURCE ----------
import java.util.Comparator;
import java.util.PriorityQueue;

public class Queue3 {

    static class Pri {
        int pri;

        public Pri(int pri) {
            this.pri = pri;
        }

        public int pri() {
            return pri;
        }
    }

    public static void main(String[] args) {
        PriorityQueue<Pri> queue = new PriorityQueue<Three.Pri>(Comparator.comparingInt(Pri::pri));
        queue.add(new Pri(3));
        queue.add(new Pri(2));
        queue.add(new Pri(1));
        queue.forEach(p -> System.out.println(p.pri));
    }
}

---------- END SOURCE ----------

FREQUENCY : always