Returns false if the iteration is complete, true otherwise.
Usually iteration is considered to be complete if all elements of the
underlying data structure were handled through calls to next(). However,
in custom iterators any logic may be used to determine the completion
state.
next ():T
Returns the current item of the Iterator and advances to the next one.
This method is not required to check hasNext() first. A call to this
method while hasNext() is false yields unspecified behavior.
On the other hand, iterators should not require a call to hasNext()
before the first call to next() if an element is available.