Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

int total = 0;
for (int i : v)
total += i;
6.3.3 Implementing Iterators
One way to implement an iterator for a collection of elements is to make a
"snapshot" of it and iterate over that. This approach would involve storing the
collection in a separate data structure that supports sequential access to its elements.
For example, we could insert all the elements of the collection into a queue, in
which case method hasNext() would correspond to !isEmpty() and next()
would correspond to enqueue(). With this approach, the method iterator()
takes O(n) time for a collection of size n. Since this copying overhead is relatively
costly, we prefer, in most cases, to have iterators operate on the collection itself, not
a copy.
In implementing this direct approach, we need only to keep track of where in the
collection the iterator's cursor points. Thus, creating a new iterator in this case
simply involves creating an iterator object that represents a cursor placed just before
the first element of the collection. Likewise, performing the next() method
involves returning the next element, if it exists, and moving the cursor just past this
element's position. Thus, in this approach, creating an iterator takes O(1) time, as do
each of the iterator's methods. We show a class implementing such an iterator in
Code Fragment 6.14, and we show in Code Fragment 6.15 how this iterator could
be used to implement the iterator() method in the NodePositionList
class.
Code Fragment 6.14:
Position List.
An element iterator class for a
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