RFR:8146218: Producing streams in java.time?

Tagir F. Valeev amaembo at gmail.com
Thu Jan 28 04:28:26 UTC 2016


It should be noted that there's already a precedent in JDK where
method returning stream is subclassed and returns the stream of more
concrete objects. I'm speaking about ZipFile and JarFile:

public class ZipFile {
   public Stream<? extends ZipEntry> stream() {...}

public class JarFile extends ZipFile {
   public Stream<JarEntry> stream() {}

Such generic stream declaration adds some difficulties for ZipFile
users. For example, consider this question:
So in general I would like to avoid Stream<? extends ChronoLocalDate>.

With best regards,
Tagir Valeev.

RR> Hi Stephen, Tagir,

RR> On 1/27/2016 10:30 AM, Stephen Colebourne wrote:
>> On 27 January 2016 at 15:13, Roger Riggs <Roger.Riggs at oracle.com> wrote:
>>> On 1/26/2016 8:57 AM, Stephen Colebourne wrote:
>>>> Thus, adding the ChronoLocalDate methods later will make two additional
>>>> methods available on LocalDate (as they will not override).
>>> Since all the calendars are built on the same 24hour days and epochDays, the computations
>>> result would be the same regardless of the Chronology.
>>> The existing LocalDate.until, compareTo, isBefore, isAfter, isEqual methods already use the
>>> ChronoLocalDate argument type to avoid having double the signatures.
>>> Modifying the type of the argument to be ChronoLocalDate would not modify the semantics
>>> and would make it possible to avoid extra methods in the future.
>>> I recommend changing the argument to ChronoLocalDate be consistent with the existing
>>> until method to keep the option open for a possible addition to ChronoLocalDate
>> The LocalDate::datesUntil(ChronoLocalDate) method internals would be
>> unaffected as it operates off toEpochDay(). Worth noting that an
>> abstraction on the ChronoLocalDate interface would have to return
>> Stream<? extends ChronoLocalDate>.
RR> Right,  Interestingly, none of the tests explicitly depend on the return
RR> type of Stream<LocalDate>
RR> and only use methods that are in ChronoLocalDate.   (Based on a quick 
RR> prototype).

RR> But its enough to suggest that there should be some additional test or
RR> use of the compile time types.

RR> A Stream<ChronoLocalDate> would be inconvenient and counter intuitive.
RR> That's enough of a reason for me to keep the current signatures.

RR> Thanks for the comments, Roger

>> A LocalDate::datesUntil(ChronoLocalDate, Period) method would however
>> contain a mixture of Chrono and ISO specific types. Given how the
>> internals of the method depend on access to Period specific concepts
>> abstracting to ChronoPeriod would not be pleasant (if possible) As
>> such, this signature seems unwise.
>> But that gives two types of signature - an abstracted one and a specific one:
>> LocalDate::datesUntil(ChronoLocalDate)
>> LocalDate::datesUntil(LocalDate, Period)
>> Again, it isn't clear that is better.
>> Stephen

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