<i18n dev> [15] RFR: 8244152: Remove unnecessary hash map resize in LocaleProviderAdapters

[Peter Levart]

Hi Naoto,

On 4/30/20 12:18 AM, naoto.sato at oracle.com wrote:
> Hello,
>
> Please review this small fix to the following issue:
>
> https://bugs.openjdk.java.net/browse/JDK-8244152
>
> The proposed changeset is located at:
>
> https://cr.openjdk.java.net/~naoto/8244152/webrev.00/
>
> The hash map used there didn't have initial capacity, even though the 
> exact numbers are known.


Well, it has to be calculated 1st (countTokens), but I guess this pays 
off when HashSet (the backing HashMap) does not have to be rehashed then.

The expression you use:

     Math.max((int)(tokens.countTokens() / 0.75f) + 1, 16)

...has a minimum value of 16. Why is that? 16 is just HashMap's default 
initialCapacity if not specified explicitly. But if you only want to 
store say 1 entry in the map, you can specify 2 as initialCapacity and 
HashMap will happily work for such case without resizing.


So you could just use:

     (int)(tokens.countTokens() / 0.75f) + 1

And even this expression is sometimes overshooting the minimal required 
value by 1 (when # of tokens is "exact" multiple of 0.75f, say 6). I 
think the following could be used to optimally pre-size the HashMap with 
default load factor 0.75:

     (tokens.countTokens() * 4 + 2) / 3


Regards, Peter

>
> Naoto