----- Mail original ----- > De: "Peter Levart" <peter.lev...@gmail.com> > À: "Remi Forax" <fo...@univ-mlv.fr>, "Cyrus Vafadari" <cvafad...@gmail.com> > Cc: "core-libs-dev" <core-libs-dev@openjdk.java.net> > Envoyé: Samedi 28 Septembre 2019 10:38:43 > Objet: Re: RandomAccess Interface and List Heirarchy
> On 9/25/19 12:15 PM, Remi Forax wrote: >> that said, i believe we should deprecate LinkedList (and any other List >> implementation that doesn't implement RandomAccess) because there are too >> much >> code out there that suppose that list.get() is O(1). > > Hi Remi, > > Deprecating LinkedList as a whole is maybe to harsh. LinkedList is a > List, but it is also the only JDK implementation of single-threaded > linked Deque, which, although a retrofitted feature, is a perfectly > fitted feature of LinkedList. That brings me to the question: Is it > possible and how to deprecate only one aspect of a particular > implementation - in this case the List interface of the LinkedList? In > this concrete case, and also because it would be strange to have a class > called LinkedList implementing only Deque interface, it may be an > alternative to 1st create a replacement in the form of LinkedDeque > implements Deque, and then deprecating the whole LinkedList. > > As always there are pros and cons to a particular "solution": > > 1. Do nothing > pros: > - no refactoring of old code needed > cons: > - performance problems continue as inexperienced programmers couple > LinkedList with typical indexed accesses of List interface > - hard discoverability of single-threaded "linked" Deque implementation > continues - LinkedList is not a name that comes to mind when searching > for Deque implementation - this is less of a problem nowadays as we have > tools like Ctrl-H in IDEA, ... > > 2a. Deprecate the List aspect of LinkedList and eventually remove the > List interface from the LinkedList > pros: > - performance problems eventually solved > - at least some of the usages of LinkedList would remain valid: Deque<T> > d = new LinkedList<>(); > cons: > - compatibility risk - all uses of LinkedList that assume it implements > List interface will have to be refactored > - hard discoverability of single-threaded "linked" Deque implementation > continues - LinkedList is not a name that comes to mind > > 2b. Deprecate the List aspect of LinkedList with not planned removal of > the List interface from the LinkedList > pros: > - performance problems eventually solved > - at least some of the usages of LinkedList would remain valid: Deque<T> > d = new LinkedList<>(); not even warnings suppression would be needed > - no immediate compatibility risk - only suppressing warnings may be > needed in short term > cons: > - hard discoverability of single-threaded "linked" Deque implementation > continues - LinkedList is not a name that comes to mind > > 3. Create a replacement LinkedDeque implementation of Deque and > deprecate LinkedList (with no planned removal) > pros: > - performance problems eventually solved as new code typically would > refrain from using LinkedList for the List purpose and would start using > LinkedDeque for the Deque purpose > - no refactoring of old code needed (at least not in the near future) > - better discoverability of single-threaded "linked" Deque implementation > cons: > - new type to learn > - code using new type would not compile/run on old JDKs - adoption rate > of new type would be slow > > > 2b is most promising IMO. But is there an effective way to deprecate the > List aspect of the LinkedList? What would be needed is a particular use > of @Deprecated annotation that would cause usages like this: > > List<T> l = new LinkedList<>(); > > produce compile-time deprecation warnings, but usages like this: > > Deque<T> d = new LinkedList<>(); > > not produce warnings. > > The 1st thing that comes to mind is adding a TYPE_USE to the list of > @Target(s) of the @Deprecated annotation and then using it like this: > > public class LinkedList<E> > extends AbstractSequentialList<E> > implements @Deprecated List<E>, Deque<E>, Cloneable, > java.io.Serializable > > > Would this make sense? For 2b, you don't have to have a syntax for that, it can be one line of code in the compiler. Introducing an exotic syntax for an exotic use case is generally not a good idea, it's better to solve it in an ad hoc way. I don't think we need to find a replacement to LinkedList seen as a Deque given that perf wise it's always better to use an ArrayDeque instead. But i may be wrong. so i'm more for option 0, deprecate LinkedList, provide no replacement for LinkedList as a Deque. > > > Regards, Peter regards, Rémi
