This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
poll method Retrieves and removes the head of this queue . so when you remove an element from collection at the time of looping you get ConcurrentModificationException. to remove an element while looping use Iterator instead.