priority queue doubt

[aslika bahini]

Priority queue

  
   import java.util.*;
public class PqTestJR {
public static void main(String[] args)
 {
PriorityQueue<Integer> pq1 = new PriorityQueue<Integer>();

pq1.add(5);
pq1.add(4);
pq1.add(3);
pq1.add(2);
pq1.add(1);
pq1.add(0);
 
System.out.println("Adding");
for(int x : pq1)
{

System.out.println(x);
}
System.out.println("after polling");
 

  

Adding
0
2
1
5
3
4
after polling
0
1
2
3
4
5
why the output for adding is 0 2 1 5 3 4?(what order it is?).
I guess while adding/offering it has to be in sort order.

or poll() does the sort order and removes the highest priority element.
correct me!

Thanks
samura

[aslika bahini]

public PriorityQueue(int initialCapacity,
Comparator<? super E> comparator)

what is the initialCapacity?
The API says it's the initialCapacity for the pq1(reference of
priorityqueue)
priorityQueue pq1 = new PriorityQueue(10,pqs)
what it does here? by giving the value 10..


I am little confused with this

[Prasanna Rajaperumal]

Hi,

Good Reason to be confused. Priority queue is implemented as Heap data structure. I do not know the exact details of the implementation. But with a min heap structure only one thing is assured, root has the minimum.

So after you poll the order you get 1, 2, 3, 4, 5 is pure coincidence. It could have been in any order with 1 as the root (first element).

Still confusing
1. read about heaps
2. Read how heaps are impemented in a queue
3. Look at priorityqueue fixup method.

0 will be polled out.