ConcurrentModificationException and for loops

[naveen yadav]

For given code

PriorityQueue<String> pq = new PriorityQueue<String>();
	pq.add("c");
	pq.add("b");	
	pq.add("a");
	pq.offer("d");
	pq.add("e");	
	pq.offer("f");
	pq.add("f");

The following code does not throw ConcurrentModificationException and run fine , I perfectly understand as ConcurrentModificationException is thrown when a thread iterating over it AND modifying it.
By iterating I means specifically using Iterator not using for loops

for(int i=0; i<8; i++)
{
System.out.println(pq.poll() );   //modifying but not Iterating
}

But here , it throws ConcurrentModificationException. I dont know why ?

for(String str:pq)
{
System.out.println(pq.poll() ); 

}

Regards
naveen

[Harsha Smith]

I perfectly understand as ConcurrentModificationException is thrown when a thread iterating over it AND modifying it.

using enhanced for loop...you are iterating through the collection and by calling poll(), you are modifying it. And yes priority queue is a collection

[Stephan van Hulst]

Harsha is correct. The enhanced for loop can only be used on arrays and subtypes of Iterable. The enhanced for loop will use the iterator to iterate through all the elements, so it's always a bad idea to remove elements from a collection using an enhanced for loop. Instead, you should use the normal for-loop, with the iterator:

for(Iterator<String> it = pq.iterator(); it.hasNext();) {
  String str = it.next();
  System.out.println(str);
  it.remove();
}

[naveen yadav]

i mistaken foreach() loop as a normal for() loop. .
Thanks for clearing this.



Regards
naveen