Change a collection while you're iterating...

Question

I read from somewhere that changing a Collection while you're iterating with an Iterator would risk a ConcurrentModificationException, but the source didn't include an example code to show this so I don't fully understand it. Could anyone give an example code when this would happen? Thanks

Answer 1

Don't use this code! This is an example how you'll get a ConcurrentModificationException.
List<String> l = new ArrayList<String>();
l.add("foo");
l.add("bar");
l.add("foobar");
for (String s : l) {
  System.out.println(s);
  l.remove("bar");
}