Throwing ConcurrentModificationException

Question

Hi,
I am implementing an Iterator and wish to throw the ConcurrentMoficationException when the underlying list is modified. I do this by keeping track of modCount variable in the iterator implemention and throw the exception if the modcount has changed after the iterator is created. It works fine on NT and gives runtime
Exception in thread "main" java.lang.IllegalAccessError: try to access
field java.util.AbstractList.modCount from class
oracle.tip.repos.core.driver.AssociationList$ItrHere AssociationList is my implementation of ArrayList.
In the iterator
private class Itr implements Iterator {
int firstModCount = modCount;
public Object next() throws ConcurrentModificationException {
// after the iterator is created list has been modified, throw
// concurrent modified exception
int newModCount = modCount;
if (firstModCount != newModCount)
throw new ConcurrentModificationException();
This code executes in NT 4.0 without any problem only on solaris I get the above runtime exception.
Could this be a bug ?
Any pointers on troubleshooting this problem ?
thanks
Poornima

Answer 1

The comments so far make sense in that it is a scoping issue. It is indeed strange that it is platform-specific. You could perhaps provide a workaround by creating a private accessor method for the iterator implementation to use. Something like
private int getModCount() {
    return modCount;
}should work OK. Then call getModCount in your iterator rather than accessing modCount directly.
I would make your new next() code look like this:
public Object next() throws ConcurrentModificationException {
    if (firstModCount != getModCount()) {
        throw new ConcurrentModificationException();
    /* the rest of your implementation */
}BTW, when you post your code, you might want to use code and /code tags (with square braces around them) in order to preserve your formatting.