Neil Veebrun

Hi Stephan,

Thanks for the helpful and quick reply. Your advice to return a new iterator every time on the iterator() method has fixed the problem. I no longer get an exception.

Cheers,

Neil

Hi there,

I'm fairly new to programming. I was hoping for some help understanding where I might be going wrong when I inherit from Iterator to make a "safe" iterator, please. This is one that can be used by a client object to iterate through the collection, but not remove anything from it.

When I run my program, I get a ConcurrentModificationException as the Client object's printProducts() method is called and I'm not sure why. Here is the relevant code:

public class SafeIterator implements Iterator<Product> { private Iterator<Product> it; public SafeIterator(List<Product> list) { it = list.iterator(); } public boolean hasNext() { return it.hasNext(); } public Product next() { return it.next(); } public void remove() { throw new RuntimeException("remove attempted"); } } public class Catalogue implements Iterable<Product>{ private List<Product> products; private Iterator<Product> it; public Catalogue(){ products = new ArrayList<Product>(); it = new SafeIterator(products); Product prod1 = new Product("CD"); Product prod2 = new Product("DVD"); Product prod3 = new Product("Blu-Ray"); products.add(prod1); products.add(prod2); products.add(prod3); } public int getSize(){ return products.size(); } @Override public Iterator<Product> iterator() { return it; } } public class Client { private Catalogue cat; public Client(){ cat = new Catalogue(); printProducts(); } public void printProducts() { for (Product product : cat){ System.out.println(product); } } }

And this is the exception:

Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:782)
at java.util.ArrayList$Itr.next(ArrayList.java:754)
at SafeIterator.next(SafeIterator.java:11)
at SafeIterator.next(SafeIterator.java:1)
at Client.printProducts(Client.java:16)
at Client.<init>(Client.java:8)
at Main.main(Main.java:8)

Help much appreciated.

Thanks,

Neil