For classes implementing abstract data types such as stacks, queues, lists, etc. that store collections of items, the Iterator interface provides a common way to access the items one at a time independent of the underlying implementation of the class.

public class Iterator<E>
{
  public boolean hasNext();
  public E next();
  public void remove(); 

}

The remove() method is "optional". T should throw UnsupportedOperationException if isn't implemented to actually remove an item.

But how do you get an Iterator for a Stack, Queue, or LinkedList?