The Iterator is not implemented as an
indexed loop, at least not in Sun Java. The collection 
always has a
getter armed with the iterator's next value. Much of the 
collection's
internal implementation is done via the iterator. But the 
pieces of
ArrayList that are optimized for speed, skip bounds 
checking and use int
array offsets to do their work.
I would like to know what is the difference between these 2.
>
> ArrayList list = new ArrayList
>
> for(int i=0; i<list.size(); i++){
> //do stuff
> }
>
> Iterator i = list.iterator();
>
> while(i.hasNext(){
> do stuff
> }

Iterator is used in Collection objects,but for is used for 
variables.

In iterator the remove() is available to remove the
content/item but in for loop  remove() not available.

The major difference is Iterator doesn't output the list we 
are iterating in sequence.
where as in for we structure it to print in sequence.