RFR: 8300818: Reduce complexity of padding with DateTimeFormatter [v2]

[Sergey Tsypanov]

On Mon, 23 Jan 2023 11:34:27 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> The modified code is called only when a user explicitly calls `padNext(int, char)`, i.e. if I modified the example snippet as
>> 
>> DateTimeFormatter dtf = new DateTimeFormatterBuilder()
>>   .appendLiteral("Date:")
>> //.padNext(20, ' ')
>>   .append(DateTimeFormatter.ISO_DATE)
>>   .toFormatter();
>> String text = dtf.format(LocalDateTime.now());
>> 
>> there's no regression.
>> 
>> Right now I cannot build ad-hoc JDK with my changes and check it with JMH, so I'd convert this to draft until I can verify it
>
> Meant that you should verify that something like this, which just add a little padding, doesn't regress with your changes: 
> 
> DateTimeFormatter dtf = new DateTimeFormatterBuilder()
>     .appendLiteral("Year:")
>     .padNext(5)
>     .appendValue(ChronoField.YEAR)
>     .toFormatter();
> ... 
> dtf.format(LocalDateTime.now());
> 
> And similar for effectively no padding (`.padNext(4)` in the above example). As this API might often be used to ensure short 2-4 char fields are correctly padded I think it's important that we're not adding overhead to such use cases.

Added benchmark for this

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PR Review Comment: https://git.openjdk.org/jdk/pull/12131#discussion_r1147980908