[threeten-dev] [threeten-develop] #176 Cnveret ZoneRules from interface to calss

[Stephen Colebourne]

On 21 December 2012 01:08, Xueming Shen <xueming.shen at oracle.com> wrote:
> I'm not sure if we want to have an extra public factory method of(ZoneOffset)
> to simply for better memory performance when being created from
> ZoneOffset.getRules(), which probably will not happen in normal scenario.

ZoneOffset.getRules() will be called a lot via ZDT. It is vital to
have the extra factory so we can optimise later. Just constructing the
empty lsts and passin 5 arguments rather than 1 is an overhead.

Stephen


> The webrev has been updated for your other comments.
>
> I will try to see if we can have a better option.
>
> -Sherman
>
> On 12/20/2012 04:52 PM, Stephen Colebourne wrote:
>> On 21 December 2012 00:22, Xueming Shen<xueming.shen at oracle.com>  wrote:
>>> On 12/20/2012 04:07 PM, Stephen Colebourne wrote:
>>>> The rules for offsets are created and thrown away rapidly, whereas
>>>> ZoneId rules are cached. Thus I think we should keep the special
>>>> implementation for offsets (as a hidden inner class). It is likely to
>>>> have much better performance and garbage collection because it is
>>>> simpler.
>>> Agreed. But the problem is that we want to return a ZoneRules, which is
>>> supposed to be final... There should be not too big impact to the memory
>>> footprint, given those a singleton empty list or zero-length array, but yes,
>>> ideally we can have a simple representation for this special case.
>> A non-final class with a package-scoped construcor can be considered
>> to be immutable if all the fields it holds are declared final.
>>
>> We're talking about 16 extra bytes per instance created, which isn't
>> ideal. If the other fields were null it may help the gc more than
>> having empty arrays.
>>
>> Perhaps we could invert the internal hierarchy. Have the simple
>> implementation as ZoneRules and the complex implementation as the
>> subclass? A little weird, but effective in memory usage, and hidden
>> from most users.
>>
>> I'd suggest you start by adding the extra factory method, and maybe
>> push that. The internal optimisation can then come later.
>>
>> Stephen
>>
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