Iterator.next() throws java.util.ConcurrentModificationException

Question

Hello, I have a set and an iterator defined like this:
HashSet<JFrame> set = new HashSet<JFrame>();
Iterator<JFrame> iterator = set.iterator();
Then later I add frames like this:
set.add(jFrame);
Then later when I try to call:
iterator.next();
I get ConcurrentModificationException. But I only call this next() method one time and only.
I can call hasNext() method without a problem, but not next().
How do I call next() without an exception??
Mark

Answer 1

create an iterator and then after this you change the collection? does this sound safe?(...)after getting the iterator, don't modify the set (with exception as per api) and expect the iterator to work.
Well, I think you are making fun of me here. It's OK, I don't mind, but I want to disagree with your reasons.
"Does this sound safe?" Yes, why not? The iterator could refer to the set, whatever its contents. You could add to the set and, and then remove from it by iterator.next(), and add and remove... As long as you synchronise all these things (and I do), there is no general reason why this would be a bad thing.
But of course, the API does prohibit that explicitly, you are right. It's just that when you naturally expect certain behaviour, you don't read all of the documentation.
And then when ConcurrentModificationException happens, this exception name does not reflect what happens, as I said, I am not concurrently modifying anything in multiple threads. So the name of the exception threw me off track and I did not think it was the order of the operations that I did wrong.
Anyway, thank you very much for help.