Container exercise 9,  * @author zguo6x
 * Exercise 9: (4) Modify innerclasses/Sequence.java so that Sequence works with an
Iterator instead of a Selector.
* In Sequence.java, there are two way to provide Iterator:
* 1: return Arrays.asList(items).iterator();
* 2: return (new ArrayList(Arrays.asList(items))).iterator();
* Two difference between these method, method 1 avoid provide a variable in size result, Sequence store array, array cannot be resize, I think this is better.
* method provide a Arraylist that can be changed
* please also do not write your own Iterator, because ArrayList and LinkedList is easy to use