Enumeration adapters in SE 8

[Collin Fagan]

There was a time where it was considered best practice to return an iterator
instead of a collection.  There are now many apis and legacy code that are
not compatible with the for each loop.

I think even if there are only a few places in the jdk where this would
apply it would still be convenient in the wild.
Collin

On Wed, Aug 24, 2011 at 4:58 PM, Colin Decker <cgdecker at gmail.com> wrote:

> I've come across various scenarios. One example is
> javax.swing.tree.DefaultMutableTreeNode. It has numerous methods that
> return
> Enumerations, including:
> - children
> - depthFirstEnumeration
> - breadthFirstEnumeration
> - preorderEnumeration
> - postorderEnumeration
> - pathFromAncestorEnumeration
>
> I've created a utility class with methods to return Iterables for each of
> these types of Enumerations for convenience, but it would be much nicer to
> just use a method reference.
>
> Deque's descendingIterator() method is a more modern good candidate for
> treating as an Iterable. See this question on StackOverflow:
>
> http://stackoverflow.com/questions/3883131/idiomatic-way-to-use-for-each-loop-given-an-iterator
>
> --
> Colin
>
>
> On Wed, Aug 24, 2011 at 5:45 PM, Ben Evans <benjamin.john.evans at gmail.com
> >wrote:
>
> > Hi Dan,
> >
> > On Wed, Aug 24, 2011 at 7:10 PM, Dan Smith <daniel.smith at oracle.com>
> > wrote:
> >
> > > I was pointed to some comments on core-libs about adapting Enumerations
> > to
> > > for loops in SE 8.  (Sorry for the new thread -- I wasn't subscribed.)
> >  It
> > > turns out lambdas + extension methods will make this very easy.
> > >
> > > In the API:
> > >
> > > interface Enumeration<E> extends Iterator<E> {
> > >  boolean hasMoreElements();
> > >  E nextElement();
> > >  boolean hasNext() default #hasMoreElements;
> > >  E next() default #nextElement;
> > >  void remove() default { throw new UnsupportedOperationException(); }
> > > }
> > >
> > > Note that Iterable is a function type -- a thunk producing an Iterator
> --
> > > and so we can express Iterables with lambdas and method references.
>  It's
> > > becoming clear that a for loop should provide a target type for these
> > > things, so that will probably be part of the SE 8 feature set.
> > >
> > > With a method reference:
> > >
> > > Hashtable<String,Object> h = …;
> > > for (String s : h#keys) { … }
> > >
> >
> > I'm struggling to see where this might be useful. This example is
> obviously
> > too trivial and would add nothing, but I can't see to come up with any
> more
> > extensive example where having a method reference in this position would
> be
> > actually useful.
> >
> > Can someone else provide a more compelling example for a for loop taking
> a
> > method reference?
> >
> > Thanks,
> >
> > Ben
> >
> >
>
>