Help me with Java iterators, please.

Question

I'm supposed to convert an algorithm that's working on a simple array to work on a linked list, but I have to keep it with the same complexity. I've tried using iterators to replicate the nested fors, but I'm running into an issue. For instance:
ListIterator it = listname.listIterator();
Listiterator it2 = it;
System.out.println(it.next());
System.out.println(it2.next());
System.out.println(it.next());
System.out.println(it2.next());With a list of [5, 4, 3, 2, 1], I'd get 5, 4, 3 and 2 instead of 5, 5, 4 and 4. The problem is that the iterators aren't moving idenpendently. I guess a shallow copy was created instead of a deep copy. This is pretty dumb from where I'm standing, because it's pointless to copy the iterator if they aren't going to be independant.
Anyway, is there a way to make it so that I can copy a iterator while keeping him independant from its source? I can't create another iterator from scratch and traverse the list.
I've also tried doing a new class implementing ListIterator and Cloneable, but this:
IteratorClass it3 = listname.IteratorClassgave me an error. I did the class so it was abstract and I wouldn't have to implement methods that I wouldn't be using, so I'm not sure if that was the problem. I'm new to Java, so I'm pretty confused to be honest. I know cloneable is supposed to allow me to create a deep copy, but since I'm calling the ListIterator from the LinkedList, I'd have to implement my own kind of iterator with Cloneable and ListIterator and then create a subclass of LinkedList?
Anyway, thanks in advance.

Answer 1

BananaPow3 wrote:
I'm supposed to convert an algorithm that's working on a simple array to work on a linked list, but I have to keep it with the same complexity. I've tried using iterators to replicate the nested fors, but I'm running into an issue. For instance:
ListIterator it = listname.listIterator();
Listiterator it2 = it;
System.out.println(it.next());
System.out.println(it2.next());
System.out.println(it.next());
System.out.println(it2.next());
What's the point of it2? The above code is identical to
ListIterator it = listname.listIterator();
System.out.println(it.next());
System.out.println(it.next());
System.out.println(it.next());
System.out.println(it.next());
With a list of [5, 4, 3, 2, 1], I'd get 5, 4, 3 and 2 instead of 5, 5, 4 and 4. Because you're calling next on the same iterator each time. The = opeator never copies objects in Java, only references.
Iterator it2 = it;All that line does is copy the value from variable it into variable it2. That value is a refrence. Both variables now refer to the same Iterator object.
The problem is that the iterators aren't moving idenpendently. I guess a shallow copy was created instead of a deep copy. This is pretty dumb from where I'm standing, because it's pointless to copy the iterator if they aren't going to be independant.You didn't copy an Iterator. You copied a reference.
If you want a second ListIterator over that list, then do ListIterator it2 = listname.listIterator();(By the way, why are you using ListIterators instead of just Iterators? Will you be going backward as well?
Anyway, is there a way to make it so that I can copy a iterator while keeping him independant from its source? Nope.
I can't create another iterator from scratch and traverse the list.Why not?
Edited by: jverd on Aug 9, 2008 2:50 PM