Iterators
---------
A simple example of an iterator. 

  > java Test

We have the generic list class GList<E> with the methods

  - getHead
  - addFirst
  - removeFirst
  - isEmpty
  - toString

But how do we iterate over GList L? We might like to do as follows

  for (int i=0;i<L.size();i++) doSomethingWith(L.get(i));

The L.get(i) could be O(n) complexity, or maybe even worse. So what we do is
create an Iterator.

We then have the iterator class GIterator. An Iterator is an interface (a contract/API), 
has the methods

   - hasMore
   - next
   - remove

and we implement this in the class GIterator

In the GList class we have a method iterator() that produces a GIterator
and then we can iterate over elements of the GList as follows

                GIterator<String> iter = new GIterator<String>(L);
		while (iter.hasNext()) System.out.println(iter.next());

Ideally we would like to use the foreach construct

		 for (Node<String> x : L) System.out.println(x); 

however to do this we need to respect class heirarchy to allow the compiler
to translate the foreach into the declaration and while above.
Therefore what we have done is maybe not "java etiquette" but it will result in the
same code. 

For the true java etiquette see Chap6

Patrick Prosser
2/7/10