A developer-friendly string representing the instance. Concatenates the name of the concrete class of the instance with the hash of the instance. Subclasses are encouraged to refine this implementation to produce a more meaningful representation.

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.

An iterator for a nonempty stream must produce at least one value of type Element.