<i18n dev> RFR: 8368172: Make java.time.format.DateTimePrintContext immutable [v6]

[Roger Riggs]

On Thu, 2 Oct 2025 03:08:32 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> I propose to make j.t.f.DateTimePrintContext immutable.
>> 
>> Currently, DateTimePrintContext has only one mutable field, optional. This can be replaced by adding an optional parameter to the DateTimeFormatter.formatTo method.
>> 
>> Immutable DateTimePrintContext can be optimized by escape analysis, such as immutable object optimization.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve javadoc for optional parameter in DateTimePrinterParser#format method

And one more thought/question:
The optionality of formatting is a parameter used in the traversal of the formatting and parsing and affect nested formatting calls.  The DateTimePrintContext previously counts the depth of the nesting with >0 indicating optional.
It is the component that determines (based on optional:true) whether an absent value throws.
Was it considered to change DateTimePrinterContext.optional to `final boolean optional` and create a second instance with optional=true. 

Only the CompositePrinterParser changes the state to indicate that nested PrinterParsers are optional.
CompositePrinterParser could substitute the optional DateTimePrintContext.
That would be closer to the current design and if allow it to be immutable.

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PR Comment: https://git.openjdk.org/jdk/pull/26913#issuecomment-3361215508