Create java.util.stream.Stream from Iterator / Enumeration

[Patrick Reinhart]

Hi Paul,

I see the point, that making it too easy there.  I might have to some
little explain where I have started from. I wanted to go over all
resource URL's from a ClassLoader and read them as a Stream:

Enumeration<URL> resources =
myInstance.getClassLoader().getResources("resource.name");
Collections.list(resources).stream()....

Which will internally copy all elements right away into an ArrayList and
does more than I wanted... :-)

So, with that your good reasons in mind, in my case leaded me in a wrong
solution in the first attempt too - thanks good I looked into the source
code ;-)

In my case then is the used approach to get a Stream correct?

Cheers

Patrick



On 14.06.2016 18:26, Paul Sandoz wrote:
> Hi Patrick,
>
> Enumeration now has an asIterator method, that’s our attempt to bridge the old traversal world to the less old ( :-) ) world.
>
> Bridging the gap between the less old world and the new world (streams) is more subtle, and we have been holding out on that.
>
> We wanted to avoid providing simple methods to create a Stream from an Iterator, that might serve as an attractive nuisance e.g. Stream.of(arrayList.iterator()), rather than arrayList.stream(), and there are details of size, order etc for which any defaults might be poor or just wrong depending the Iterator’s source of elements.
>
> For example, your helper method assumes that the Iterator is covering a structure that is both immutable and ordered, but what if the Iterator was obtained from a HashSet?
>
> If we chose to provide such a helper method we would have to assume that the Iterator’s source of elements is of unknown size, order and mutability, essentially no Spliterator characteristics can be derived from the Iterator.
>
> Paul.
>
>> On 14 Jun 2016, at 01:13, Patrick Reinhart <patrick at reini.net> wrote:
>>
>> Hi there,
>>
>> I know you are busy getting the latest release ready. Still I have question according the java.util.stream.Stream's static helper methods. During my work I ran into a couple places where creating a Stream out of a Iterator or Enumeration directly would be quite handy.
>>
>> At the moment I have made me two methods like this on a helper class in oder to not duplicate the code:
>>
>>  public static <T> Stream<T> iterate(Iterator<T> iterator) {
>>    Objects.requireNonNull(iterator);
>>    return StreamSupport.stream(Spliterators
>>      .spliteratorUnknownSize(iterator, Spliterator.ORDERED | Spliterator.IMMUTABLE), false);
>>  }
>>
>>  public static <T> Stream<T> iterate(Enumeration<T> enumeration) {
>>    Objects.requireNonNull(enumeration);
>>    final Iterator<T> iterator = new Iterator<T>() {
>>      @Override
>>      public boolean hasNext() {
>>        return enumeration.hasMoreElements();
>>      }
>>
>>      @Override
>>      public T next() {
>>        return enumeration.nextElement();
>>      }
>>    };
>>    return iterate(iterator);
>>  }
>>
>>
>> My question is now, if it would be worth while having something like this on the Stream itself?
>>
>>
>> Cheers
>>
>> Patrick