priority queue - Retrieve item from the middle of a PriorityQueue in Java -

given following code:

import java.util.*;  class simpletest {     public static void main(string[] args) {         priorityqueue<integer> pq = new priorityqueue<>();          pq.add(1);         pq.add(2);         pq.add(3);         pq.add(4);         pq.add(5);         pq.add(6);         pq.add(7);          int index = 0;         int middlenumber = 0;         iterator = pq.iterator();          //is number odd         if(pq.size() % 2 != 0) {             system.out.println(pq.size());              //keep removing queue until reached queuesize/2 (rounded up)             while(it.hasnext() && index++ <= ((pq.size() >> 1) + 1)) {                 middlenumber = pq.poll();             }             system.out.println("the middle number is: " + (float)middlenumber);         }             } } 

this works on odd numbers, not others, , fail see why.

given queue of 7 items, code above returns 4 in middle of queue.

but if try queue 9 elements (1-9). returns 4, when should 5.

why happen?

the main problem line:

                middlenumber = pq.poll(); 

decrements size of queue, affects meaning of line:

            while(it.hasnext() && index++ <= ((pq.size() >> 1) + 1)) { 

then there secondary problems — while expression wrong written — think because tried tweak while work case queue started 7 elements, not understanding underlying bug.

instead, should precompute index want, , poll point:

int indexofmiddlenumber = pq.size() / 2; (int index = 0; index < indexofmiddlenumber; ++index) {     pq.poll(); } int middlenumber = pq.poll(); 

(note there's no use iterator, , it's bad idea call it.hasnext() in loop that's modifying underlying collection. i'm surprised priorityqueue isn't giving concurrentmodificationexception this.)