RFR 7065380 : Allow Collections.sort to sort Collections.singletonList() result

[Vitaly Davidovich]

+1.  A no-op sort() on an emptyList or singletonList() behaves in an
intuitive manner, IMHO.  If the concern is that sort() will hide user bugs,
well my answer would be that sort()'s job is just that: sort the collection
-- it's not a defense mechanism for catching unrelated user bugs.


On Thu, Mar 1, 2012 at 5:02 PM, Mike Duigou <mike.duigou at oracle.com> wrote:

> I always read @throws declarations as "if thrown then description was the
> cause" rather than "will be thrown if description". A minor difference in
> interpretation that can sometimes be useful.
>
> For this particular case the restriction on sort() seems to serve only to
> blunt the usefulness of Collections.emptyList and singletonList(). I'd
> prefer to bend the rules slightly rather than requiring developers to use
> empty and singleton ArrayLists.
>
> Mike
>
> On Mar 1 2012, at 13:29 , Colin Decker wrote:
>
> > Doesn't this break the contract of the method? It specifies that it
> throws UnsupportedOperationException if the specified list's list-iterator
> does not support the set operation. Its Javadoc body also states that the
> list must be modifiable. (Though sort() already succeeds for an emptyList()
> despite it not supporting set.)  It seems to me that this just hides
> programmer error. Anyone who passes an unmodifiable singleton list to
> sort() is treating it as a modifiable list in their code. Rather than
> succeeding despite that, I'd think it might be preferable for the call to
> fail so the programmer is alerted to that error in their assumptions so
> they can correct it before it bites them elsewhere.
> >
> > --
> > Colin
> > 5
> >
> > On Thu, Mar 1, 2012 at 2:40 PM, Mike Duigou <mike.duigou at oracle.com>
> wrote:
> > Hello all;
> >
> > Currently Collections.sort() refuses to sort the lists which result from
> calling Collections.singletonList(). This makes some sense because the
> singleton lists are immutable but they are also alway sorted.
> >
> > This patch allows Collections.sort() to be used with empty and singleton
> lists of all types. A short circuit return is provided for lists of length
> 0 and 1 as they are already sorted.
> >
> > WEBREV @ http://cr.openjdk.java.net/~mduigou/7065380/0/webrev/
> >
> > For the unit test ignore the diffs and view the "New" file--webrev
> doesn't understand "hg copy".
> >
> > Thanks,
> >
> > Mike
> >
>
>


-- 
Vitaly
617-548-7007 (mobile)