CODEWITHSUNDEEP
javaiteratorlinked-listsublist
WojciechKo
WojciechKo

Reputation: 1531

How to modify subList without ConcurrentModificationException?

I have a little problem with ListIterator.

I have started iterate original list [1, 4, 5], I am between 1 and 4. Then I modify list to the [1, 2, 3, 4, 5]. Now I would like to iterate rest of the original list. Here I give an example code:

public class Test {
    public static void main(String[] args) {        
        List<Integer> list = new LinkedList<Integer>();  // []
        list.add(new Integer(1));  // [1]
        list.add(new Integer(4));  // [1, 4]
        list.add(new Integer(5));  // [1, 4, 5]
        ListIterator<Integer> iterator = (ListIterator<Integer>) list.iterator();

        System.out.println(iterator.next()); // prints [1]

        // modify subList
        List<Integer> subList = list.subList(0, 2);    // [1, 4]
        subList.add(1, new Integer(2));    // [1, 2, 4]
        subList.add(2, new Integer(3));    // [1, 2, 3, 4]

        // need to print rest of oryginal list: [4, 5]
        while (iterator.hasNext())
            System.out.println(iterator.next());
    }
}

When I'm executing it I have got java.util.ConcurrentModificationException. Do you have any idea how can I do it correctly?

Upvotes: 2

Views: 2787

Answers (2)

Lone nebula
Lone nebula

Reputation: 4878

You've misunderstood the usage of list.subList.

The sublist is simply a view of a portion of the original list. If you modify the sublist, you're really modifying the original list.

What you want, is to copy part of the original list:

List<Integer> subList = new ArrayList<Integer>(list.subList(0,2));

Upvotes: 7

Zim-Zam O&#39;Pootertoot
Zim-Zam O&#39;Pootertoot

Reputation: 18148

If you make the modifications to the list through the iterator (instead of through the list) then you won't get a ConcurrentModificationException

    System.out.println(iterator.next()); // prints [1]

    iterator.add(new Integer(2)); // [1, 2, 4]
    iterator.add(new Integer(3)); // [1, 2, 3, 4]

    while (iterator.hasNext())
        System.out.println(iterator.next());

Upvotes: 1

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