Concurrent Modification Exception : adding to an ArrayList

Question

The problem occurs at ``` Element element = it.next(); ``` And this code which contains that line, is inside of an `OnTouchEvent` ``` for (Iterator it = mElements.iterator(); it.hasNext();){ Element element = it.next(); if(touchX > element.mX && touchX < element.mX + element.mBitmap.getWidth() && touchY > element.mY && touchY < element.mY + element.mBitmap.getHeight()) { //irrelevant stuff.. if(element.cFlag){ mElements.add(new Element("crack",getResources(), (int)touchX,(int)touchY)); element.cFlag = false; } } } ``` All of this is inside `synchronized(mElements)`, where `mElements` is an `ArrayList` When I touch an `Element`, it may activate `cFlag`, which will create another `Element` with different properties, which will fall off the screen and destroy itself in less than a second. It's my way of creating particle effects. We can call this "particle" `crack`, like the String parameter in the constructor. This all works fine until I add another main `Element`. Now…

Accepted Answer

ConcurrentModificationException occurs when you modify the list (by adding or removing elements) while traversing a list with `Iterator`. Try ``` List thingsToBeAdd = new ArrayList(); for(Iterator it = mElements.iterator(); it.hasNext();) { Element element = it.next(); if(...) { //irrelevant stuff.. if(element.cFlag){ // mElements.add(new Element("crack",getResources(), (int)touchX,(int)touchY)); thingsToBeAdd.add(new Element("crack",getResources(), (int)touchX,(int)touchY)); element.cFlag = false; } } } mElements.addAll(thingsToBeAdd ); ``` Also you should consider enhanced for each loop as Jon suggested.

Concurrent Modification Exception : adding to an ArrayList

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