Exception in Thread "Thread-1" Java.util.ConcurrentModificationException exception causes and workarounds

Note: Reference blog: https://www.cnblogs.com/dolphin0520/p/3933551.html
1. Abnormal recurrence in single-thread environment

    public static void Main (string[] args)  {        arraylist<integer> list = new arraylist<integer> ();        List.add (2);        iterator<integer> Iterator = List.iterator ();        while (Iterator.hasnext ()) {            integer integer = Iterator.next ();            if (integer==2) {                list.remove (integer);                Iterator.remove ();   Correct notation            }}}    

When the while (Iterator.hasnext ()) loop is traversed, only the last element of the ArrayList internal elementdata[] is allowed to be deleted, but not removed from the middle.
In the source code of Iterator.next (), the method is executed first: Checkforcomodification (); This method:

final void Checkforcomodification () {            if (modcount! = expectedmodcount)                throw new Concurrentmodificationexception ();        }

Only if the values of the two variables are equal do not error. and List.add (2) operation and List.remove (integer);   Operation will make modcount++;  But the variable expectedmodcount is the variable of the ITR subclass of the inner class, the instantiation method of the subclass is: List.iterator (); An instance object is assigned an initial value:
int expectedmodcount = Modcount; Therefore, it is not allowed to have List.add (2) operation and List.remove (integer) within the while (Iterator.hasnext ()) loop method, or it will cause expectedmodcount! = Modcount, which in turn leads to the throw of the new Concurrentmodificationexception ();

Exception in Thread "Thread-1" Java.util.ConcurrentModificationException exception causes and workarounds