How to Avoid ConcurrentModificationException When Modifying an ArrayList During Iteration?

ConcurrentModificationException while Modifying an ArrayList During Iteration

The reported exception is a ConcurrentModificationException, originating from the attempt to modify an ArrayList, mElements, while iterating over it.

Inside an OnTouchEvent handler, there's a loop iterating over mElements using an Iterator to check for specific conditions:

for (Iterator<element> it = mElements.iterator(); it.hasNext();){
    Element element = it.next();

    // Check element's position and other conditions...

    if(element.cFlag){
        mElements.add(new Element("crack",getResources(), (int)touchX,(int)touchY)); // ConcurrentModificationException occurs here
        element.cFlag = false;
    }
}</element>

However, modifying the ArrayList (by adding a new element) while iterating over it using an Iterator can cause a ConcurrentModificationException.

Solution:

To avoid this exception, one option is to create a separate list to store elements that need to be added and append those to the main list after completing the iteration:

List<element> thingsToBeAdd = new ArrayList<element>();
for(Iterator<element> it = mElements.iterator(); it.hasNext();) {
    Element element = it.next();

    // Check element's position and other conditions...

    if(element.cFlag){
        // Store the new element in a separate list for later addition
        thingsToBeAdd.add(new Element("crack",getResources(), (int)touchX,(int)touchY));
        element.cFlag = false;
    }
}

// Add all elements from the temporary list to the main list
mElements.addAll(thingsToBeAdd );</element></element></element>

Alternative Approach:

Another approach is to use an enhanced for-each loop, which iterates over a copy of the list, preventing ConcurrentModificationException:

for (Element element : mElements) {

    // Check element's position and other conditions...

    if(element.cFlag){
        mElements.add(new Element("crack",getResources(), (int)touchX,(int)touchY)); // No ConcurrentModificationException
        element.cFlag = false;
    }
}

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