Reasons why to use Iterator for List rather than for loop ?

Question

when i use the iterator and for loop for traversing through the list. it takes the same time for iterator and also for for loop. even if there is a change it is a minor millisecond difference.
what is the actual difference and what is happening behind the traversing list through iterator
if we are using we are importing extra classes ...if we are using for loop there is no need to import any classes

Answer 1

If you have an array-backed collection, like an ArrayList, then the difference between using an iterator and get() will be negligible.
However, if you have a linked list, using get() is O(n^2) whereas iterator is O(n).
So with an iterator, regardless of what your underlying data structure, a list of 100,000 elements takes 1,000 times as long to iterate over as a list with 100 elements. But using get() on a LinkedList, that same 100,000 element list will take 1,000,000 times as long as the 100 item list.
There's no real benefit to ever using get()
Side note: I've been comparing iterators to get(), not iterators to for loops. This is because whether it's a for or a while has nothing to do with whether you use an iterator or get(). The way I use iterators is for (Iterator iter = list.iterator(); iter.hasNext(); ) {
    Foo foo = (Foo)iter.next();
}