On Thu, 11 Feb 2021 04:44:08 GMT, Stuart Marks <sma...@openjdk.org> wrote:
>> src/java.base/share/classes/java/math/BigDecimal.java line 97:
>>
>>> 95: * contrast, the {@link equals equals} method requires both the
>>> 96: * numerical value and representation to be the same for equality to
>>> 97: * hold.
>>
>> Note, discussing "representation" is ok here since the context is discussing
>> the representation of BigDecimal (in contrast to the text in Comparable).
>
> It might be reasonable to add a bit of rationale here and give an example. I
> think the reason that members of the same cohort might not be considered
> `equals()` to one another is that they are not substitutable. For example,
> consider 2.0 and 2.00. They are members of the same cohort, because
>
> new BigDecimal("2.0").compareTo(new BigDecimal("2.00")) == 0
>
> is true. However,
>
> new BigDecimal("2.0").equals(new BigDecimal("2.00"))
>
> is false. They aren't considered `equals()` because they aren't
> substitutable, since using them in an arithmetic expression can give
> different results. For example:
>
> new BigDecimal("2.0").divide(new BigDecimal(3), RoundingMode.HALF_UP)
> ==> 0.7
>
> new BigDecimal("2.00").divide(new BigDecimal(3), RoundingMode.HALF_UP)
> ==> 0.67
>
> I think that's the right rationale, and a reasonable example to illustrate
> it. Edit to taste. I think it would be good to have material like this,
> though, because people's immediate reaction to BD being inconsistent with
> equals is "well that's wrong." Well, no, it's right, and I think this is the
> reason.
Added example using scale and unscaledValue.
-------------
PR: https://git.openjdk.java.net/jdk/pull/2471
