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;
    }
}

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 );

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;
    }
}

The above is the detailed content of How to Avoid ConcurrentModificationException When Modifying an ArrayList During Iteration?. For more information, please follow other related articles on the PHP Chinese website!