Hi Bernd, On Wed, Nov 15, 2017 at 7:04 AM, Bernd Eckenfels <e...@zusammenkunft.net> wrote: > I would however vote for allowing an empty list to be sorted. This is such a > common case to return a replacement empty list that it will not only > introduce changed behavior but also forces ugly code.
I think we would need to write ugly code in any case as Java 9 has now two empty list implementations: Collections.emptyList() and List.of(). Collections.emptyList().sort() does not throw an exception. List.of().sort() throws an exception. Best regards, Andrej Golovnin > > For singleton list I can kind of understand that you want to fail early, but > it could be made the same argument as for the empty case. > > In the end, if we allow one or both, it requires to be spelled out > explicitely (unfortunately a spec change, even when it is the more likely > usage already) > > Gruss > Bernd > -- > http://bernd.eckenfels.net > ________________________________ > From: core-libs-dev <core-libs-dev-boun...@openjdk.java.net> on behalf of > Martin Buchholz <marti...@google.com> > Sent: Wednesday, November 15, 2017 5:10:06 AM > To: Tagir Valeev > Cc: core-libs-dev > Subject: Re: Collections.emptyList().sort() does nothing > > Different maintainers of the core library differed on whether it's > important to pedantically check for such corner case mistakes. Recently > the trend has been to check for all errors up front, even if it ends up > making no difference. Users should not depend on the library implementer's > mood or vigilance, unless they're professional testers. > > On Tue, Nov 14, 2017 at 7:52 PM, Tagir Valeev <amae...@gmail.com> wrote: > >> Hello! >> >> According to `List.sort` specification [1] "This list must be modifiable". >> According to `Collections.emptyList` specification [2] "Returns an >> empty list (immutable)." >> >> So I assume that `List.sort` cannot be called on >> `Collections.emptyList` result. However in fact this call is allowed >> doing nothing. Is this behavior documented somehow? Can I rely that it >> will not change in future Java updates? >> >> It's even more strange with `Collections.singletonList` [3] which >> "Returns an immutable list containing only the specified object". >> Obviously I cannot do: >> >> List<String> list = Collections.singletonList("foo"); >> ListIterator<String> it = list.listIterator(); >> it.next(); >> it.set("bar"); // UOE >> >> However list.sort(null) works perfectly. On the other hand [1] clearly >> says: >> >> Throws: UnsupportedOperationException - if the list's list-iterator >> does not support the set operation. >> >> To me it seems that emptyList and (especially) singletonList >> implementation does not follow the specification. Am I missing >> something? >> >> With best regards, >> Tagir Valeev. >> >> [1] https://docs.oracle.com/javase/9/docs/api/java/util/ >> List.html#sort-java.util.Comparator- >> [2] https://docs.oracle.com/javase/9/docs/api/java/util/ >> Collections.html#emptyList-- >> [3] https://docs.oracle.com/javase/9/docs/api/java/util/Collections.html# >> singletonList-T- >>
