LinkedList iterator remove

Question

Possible Duplicate:
Efficient equivalent for removing elements while iterating the Collection

private LinkedList flights;

....

public void clear(){

    ListIterator itr = flights.listIterator();

    while(itr.hasNext()){


        flights.remove(itr.next());

    }

}

....

Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
    at java.util.LinkedList$ListItr.next(Unknown Source)
    at section1.FlightQueue.clear(FlightQueue.java:44)
    at section1.FlightTest001.main(FlightTest001.java:22)

Whats wrong with it? cant at all understand why the error is given, I am sure i have used the same code on arraylists or arrays and it has worked.

Solution

You cannot remove an item from the collection directly while iterating through the elements as this will cause a ConcurrentModificationException. Iterator.remove() is the accepted safe way to modify a collection during iteration. To avoid seeing an IllegalStateException, make sure to call Iterator.next():

while (itr.hasNext()) {
   itr.next();
   itr.remove();
}

or as you simply wish to remove all elements in the Collection, you could use:

flights.clear();

See: Efficient equivalent for removing elements while iterating the Collection