RFR(s): JDK-8214687 Optimize Collections.nCopies().hashCode()

Ivan Gerasimov ivan.gerasimov at oracle.com
Tue Dec 4 06:05:29 UTC 2018

Hi Tagir!

I think what you have in the last webrev looks good!

In CopiesList.equals() please use eq() instead of Objects.equal() (see a 
comment at the line 5345).

With kind regards,

On 12/3/18 9:22 PM, Tagir Valeev wrote:
> Hello!
> Thank you for your comments!
> Yes, deserialization will be broken if we assume that size is never 0.
> Also we'll introduce referential identity Collections.nCopies(0, x) ==
> Collections.nCopies(0, y) which might introduce slight semantics
> change in existing programs. Once I suggested to wire Arrays.asList()
> (with no args) to Collections.emptyList(), but it was rejected for the
> same reason: no need to introduce a risk of possible semantics change.
> I updated webrev with equals implementation and test:
> http://cr.openjdk.java.net/~tvaleev/webrev/8214687/r2/
> Comparing two CopiesList is much faster now indeed. Also we can spare
> an iterator in the common case and hoist the null-check out of the
> loop. Not sure whether we can rely that JIT will always do this for
> us, but if you think that it's unnecessary, I can merge the loops
> back. Note that now copiesList.equals(arrayList) could be faster than
> arrayList.equals(copiesList). I don't think it's an issue. On the
> other hand we could keep simpler and delegate to super-implementation
> if the other object is not a CopiesList (like it's implemented in
> java.util.RegularEnumSet::equals for example). What do you think?
> With best regards,
> Tagir Valeev.
> On Tue, Dec 4, 2018 at 10:56 AM Stuart Marks <stuart.marks at oracle.com> wrote:
>>>> I believe it makes sense to override CopiesList.equals()
>>> Also: contains(), iterator(), listIterator()
>> equals(): sure
>> contains() is already overridden. Not sure there's much benefit to overriding
>> the iterators.
>> s'marks

With kind regards,
Ivan Gerasimov

More information about the core-libs-dev mailing list