RFR: 8290973: In AffineTransform, equals(Object) is inconsistent with hashCode()

[Martin Desruisseaux]

On Fri, 10 Jun 2022 09:39:48 GMT, Martin Desruisseaux <duke at openjdk.org> wrote:

> `AffineTransform.equals(Object)` and `hashCode()` break two contracts:
> 
> * `A.equals(A)` returns `false` if at least one affine transform coefficient is NaN.
> * `A.equals(B)` should imply `A.hashCode() == B.hashCode()`, but it is not the case if a coefficient is zero with an opposite sign in A and B.
> 
> This patch preserves the current behaviour regarding 0 (i.e. -0 is considered equal to +0) for backward compatibility reason. Instead the `hashCode()` method is updated for being consistent with `equals(Object)` behaviour.

Hello, this is a reminder for a pull request: in the `AffineTransform` class, `hashCode()` is inconsistent with `equals(Object)`. The problem occurs with NaN and ±0 coefficients. In particular, the problem with zero values prevents the use of `AffineTransorm` as keys in `HashMap`, unless all zero values are forced to the same sign by `AffineTransform` construction or by pre-processing before using an `AffineTransform` instance as a key.

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PR: https://git.openjdk.org/jdk/pull/9121