HashSet中的并发修改异常

Question

I'm getting the Concurrent Modification Exception error with this code:

Iterator iterateBids = bidders.iterator();
     Person nextBidder;

bidders.add(bid.getBidder());

if (highestBid == null) {
    // There is no previous bid.
    highestBid = bid;
    while (iterateBids.hasNext()) {
        //nextBidder = (Person) iterateBids.next();
        ((Person) iterateBids.next()).bidUpdate(this, bid);
    }
    return true;
} else if (bid.getValue() > highestBid.getValue()) {
    // The bid is better than the previous one.
    highestBid = bid;
    while (iterateBids.hasNext()) {
        nextBidder = (Person) iterateBids.next();
        nextBidder.bidUpdate(this, bid);
    }
    return true;
}

bidders is a HashSet containing Person. The error occurs at "nextBidder = (Person) iterateBids.next();" The code looks for a bid higher than the current bid. If higher, it iterates through the bidders set and performs the bidUpdate() method.

How am I modifying and iterating at the same time?

Answer 1

Only thing I can see is that you grab the iterator before this line:

 bidders.add( bid.getBidder() );

...which is clearly a modification to bidders .

Answer 2

After getting the iterator at line 1:

Iterator iterateBids = bidders.iterator();

you are modifying the data structure at line 4:

bidders.add( bid.getBidder() );