How to avoid “ConcurrentModificationException” while removing elements from `ArrayList` while iterating it? [duplicate]

Answer 1

Use an Iterator and call remove():

Iterator<String> iter = myArrayList.iterator();

while (iter.hasNext()) {
    String str = iter.next();

    if (someCondition)
        iter.remove();
}

Answer 2

As an alternative to everyone else's answers I've always done something like this:

List<String> toRemove = new ArrayList<String>();
for (String str : myArrayList) {
    if (someCondition) {
        toRemove.add(str);
    }
}
myArrayList.removeAll(toRemove);

This will avoid you having to deal with the iterator directly, but requires another list. I've always preferred this route for whatever reason.

Answer 3

If you want to modify your List during traversal, then you need to use the Iterator. And then you can use iterator.remove() to remove the elements during traversal.

Answer 4

One alternative method is convert your List to array, iterate them and remove them directly from the List based on your logic.

List<String> myList = new ArrayList<String>(); // You can use either list or set

myList.add("abc");
myList.add("abcd");
myList.add("abcde");
myList.add("abcdef");
myList.add("abcdefg");

Object[] obj = myList.toArray();

for(Object o:obj)  {
    if(condition)
        myList.remove(o.toString());
}

Answer 5

List myArrayList  = Collections.synchronizedList(new ArrayList());

//add your elements  
 myArrayList.add();
 myArrayList.add();
 myArrayList.add();

synchronized(myArrayList) {
    Iterator i = myArrayList.iterator(); 
     while (i.hasNext()){
         Object  object = i.next();
     }
 }

Answer 6

You have to use the iterator's remove() method, which means no enhanced for loop:

for (final Iterator iterator = myArrayList.iterator(); iterator.hasNext(); ) {
    iterator.next();
    if (someCondition) {
        iterator.remove();
    }
}