ConcurrentModificationException

[James Tharakan]

       List list1= new ArrayList();
         for(int i=1;i<=10;i++)
             list1.add(i);
         
         
         List list2= list1.subList(2,10);
          list1.add(3);
         
         System.out.println(list2);  //ConcurrentModificationException
           

Why such a error is caused here??

[Ankit Garg]

From the documentation of subList method

The semantics of the list returned by this method become undefined if the backing list (i.e., this list) is structurally modified in any way other than via the returned list. (Structural modifications are those that change the size of this list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)