JavaDoc fix in java.util.Date

[Roger Riggs]

Hi Steffen,

One other oddity about the shift operators in Java, they only use the 
lower 5 bits of the shift distance argument.

So,

int x = 1024;
x >>4 == 64;  and
x >> 36 == 64;

It is unusual to specify the algorithm used for hashcodes, though in 
some cases backward compatibility has forced them to be specified.

Regards, Roger


On 4/30/25 4:37 PM, Steffen Nießing wrote:
> Thanks, haven't seen unsigned right shift before. You're right, it 
> should be fine to use the unsigned one and hence Long.hashCode for that.
>
> However, the docs should match the expression used in the 
> implementation when explicitly naming the returned expression. Should 
> we update both to Long.hashCode(this.getTime())?
>
> Cheers,
> Steffen
>
> Chen Liang <chen.l.liang at oracle.com> schrieb am Mittwoch, 30. April 
> 2025 um 22:27:
>> Well, the sign has no impact here - the most significant 32 bits 
>> duplicated from the original sign bit are immediately discarded in 
>> the subsequent int cast truncation to the least significant 32 bits. 
>> However, how there is such a difference from before OpenJDK was 
>> published is still intriguing.
>> ------------------------------------------------------------------------
>> *From:* core-libs-dev <core-libs-dev-retn at openjdk.org> on behalf of 
>> Naoto Sato <naoto.sato at oracle.com>
>> *Sent:* Wednesday, April 30, 2025 3:11 PM
>> *To:* core-libs-dev at openjdk.org <core-libs-dev at openjdk.org>
>> *Subject:* Re: JavaDoc fix in java.util.Date
>> Interestingly, the implementation of Date.hashCode() does use the signed
>> right shift ">>".
>>
>> Naoto
>>
>> On 4/30/25 1:06 PM, Chen Liang wrote:
>> > Indeed, Joe is right. Unsigned right shift does not appear often 
>> and is
>> > equivalent to signed right shift if the sign bit is 0.
>> >
>> > However, this piece of quote can get an upgrade - it can become
>> > `Long.hashCode(this.getTime())`.
>> >
>> >   *
>> >     Chen
>> >
>> > 
>> ------------------------------------------------------------------------
>> > *From:* core-libs-dev <core-libs-dev-retn at openjdk.org> on behalf of
>> > Joseph D. Darcy <joe.darcy at oracle.com>
>> > *Sent:* Wednesday, April 30, 2025 2:54 PM
>> > *To:* Steffen Nießing <zuniquex at protonmail.com>; core-libs-
>> > dev at openjdk.org <core-libs-dev at openjdk.org>
>> > *Subject:* Re: JavaDoc fix in java.util.Date
>> > Unsigned right shift is non-existent?
>> >
>> > "The operators << (left shift), >> (signed right shift), and >>>
>> > (unsigned right shift) are called the shift operators. The left-hand
>> > operand of a shift operator is the value to be shifted; the right-hand
>> > operand specifies the shift distance. "
>> >
>> > 
>> https://docs.oracle.com/javase/specs/jls/se24/html/jls-15.html#jls-15.19
>> > 
>> <https://docs.oracle.com/javase/specs/jls/se24/html/jls-15.html#jls-15.19>
>> >
>> > -Joe
>> >
>> > On 4/30/2025 12:46 PM, Steffen Nießing wrote:
>> >> Hello,
>> >>
>> >> I'm new to the OpenJDK community and plan to make my first change.
>> >>
>> >> I've found a small mistake in the documentation of
>> >> java.util.Date#hashCode(). The documentation provides a Java
>> >> expression of the returned value, which uses a non-existent operator
>> >> '>>>'.
>> >>
>> >> Now I'm searching for a sponsor for a JBS issue and the code review.
>> >> Chen Liang directed me to this mailing list to ask for sponsoring on
>> >> this topic.
>> >>
>> >> Cheers,
>> >> Steffen
>> >
>> >
>>
>
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