Is it possible that I get ConcurrentModificationException when all the methods in my program are synchronized?

Question

I get a ConcurrentModificationException even though I made all the methods of the whole program synchronized (including static methods and the main method).

I don't have hidden iterators.

1. How is that even possible?!
2. What does it mean?
3. How can I fix it?

Answer 1

1. A ConcurrentModificationException can be caused by the same thread manipulating a collection while iterating over it
2. It means don't change collections while iterating over them, except through the Iterator.remove() or ListIterator.add() methods
3. see 2.