Iteration,concurrentModifcationException in Java

Question

Hi I'm using a enhanced for loop over an ArrayList and wanted to remove some elements that contain a particular value.

When I try to do this I get the above exception. I've had a look around and it seems using a enhanced for loop while modifying the collection is a bad idea. How else would I go about this?

thanks for any help.

Answer 1

This exception may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible

Answer 2

You should get an Iterator for the collection, walk that and call the remove() method on the iterator when you want to remove an element. Please be advised that not all Iterator implementations support remove(), it's an optional method!

for(Iterator it = collection.iterator(); it.hasNext();) {
  Object element = it.next();
  if(.. should remove element ..)
    it.remove()
}

Answer 3

You can keep a list of the items to be removed, then call removeAll after the loop has finished.

Vector toRemove=new Vector();
for (Object o: array){
  if(remove(o))  toRemove.add(o);
}
array.removeAll(o);

Answer 4

You cannot use the enhanced for loop to do this as you do not have access to the Iterator being used. You need to use a regular for loop and remove elements of the ArrayList via Iterator.remove().