Iterator.remove() IllegalStateException

@rgettman answer is correct but to give you imagination.

Our collection: |el1| |el2| |el3|

when you call iterator.next() it works this way:

|el1| iterator |el2| |el3|

so it jumps over the element and return reference to the element which was jumped (|el1|). So if we called iterator.remove() now, |el1| would be removed.

It's worth to add what @PedroBarros mentioned above - you can't call iterator.remove() two times without iterator.next() between them because IllegalStateException would be thrown. Also when you create two iterators (iterator1, iterator2) then calling:

iterator1.next();
iterator1.remove();
iterator2.next();

will throw ConcurrentModificationException because iterator2 checks that collection was modified.

You haven't called next() on your Iterator, so it's not referring to the first item yet. You can't remove the item that isn't specified yet.

Call next() to advance to the first item first, then call remove().

It will also call this exeption, If you add something to the list in iterator and then after it not calling it.next() again but removing the item