The next element, or finished if there are no more elements to be iterated.

Repeated invocations of next() for a given iterator must eventually produce any given element of the stream to which the iterator belongs. A given iterator must not produce the same element of the stream more often than the element occurs in the stream.

If an invocation of next() for a given iterator produces the value finished, then every future invocation of next() for that iterator must also produce the value finished.

An iterator for a nonfinite stream may never produce the value finished.