RFR: 8261123: Augment discussion of equivalence classes in Object.equals and comparison methods [v6]

[Stuart Marks]

On Fri, 12 Feb 2021 22:52:06 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> A follow-up of sorts to JDK-8257086, this change aims to improve the discussion of the relationship between Object.equals and compareTo and compare methods. The not-consistent-with-equals natural ordering of BigDecimal get more explication too. While updating Object, I added some uses of apiNote and implSpec, as appropriate. While a signum method did not exist when Comparable was added, it has existed for many years so I removed obsolete text that defined a "sgn" function to compute signum.
>> 
>> Once the changes are agreed to, I'll reflow paragraphs and update the copyright years.
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo.

Marked as reviewed by smarks (Reviewer).

src/java.base/share/classes/java/math/BigDecimal.java line 99:

> 97:  * hold. The results of methods like {@link scale} and {@link
> 98:  * unscaledValue} will differ for numerically equal values with
> 99:  * different representations.

While this text is correct and reasonable, it doesn't really explain _why_ equals() considers the representation. One might assume incorrectly that the representation is internal only and doesn't affect computations. Of course it does affect computations, which is why I suggested the example. Maybe the example doesn't belong right here, in which case it's reasonable for this change to proceed. I think it would be good to put an example _somewhere_ of non-substitutability of numerical values with different representations. Maybe we could handle that separately.

-------------

PR: https://git.openjdk.java.net/jdk/pull/2471