RFR: 8289389: Fix warnings: type should also implement hashCode() since it overrides Object.equals() [v2]

[Kevin Rushforth]

On Mon, 11 Jul 2022 18:56:36 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> @hjohn: yes, but at a price: Object.hash(Object ...) incurs overhead by creating a temporary Object[] + boxing of a Boolean.
>
> Ah, I didn't realize you checked how this is optimized by the JIT.

In order to reduce collisions, the hash of each component is typically added to `h * 31` even when that hash is 0, whereas you skip the `h = 31 * h` in the case of null. It might not be a problem in practice, since value and origin are unlikely to collide, being of different types, but you might want to look at it.

In any case, I need to time to look at it, which I won't have until after JavaFX 19 RDP1, so let's leave this until then.

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PR: https://git.openjdk.org/jfx/pull/821