RFR: 8335637: Add explicit non-null return value expectations to Object.toString() [v4]

[Joe Darcy]

On Wed, 10 Jul 2024 05:02:36 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Make well-behaved implementation expectations of Object.{toString, hashCode} explicit.
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Narrow scope of the change.

I'd like to get portions of this change in JDK 23 as well as 24. As the quality of implementation discussion on cyclic data structures, etc. looks like it needs more discussion before reaching consensus, I've filed JDK-8336043 for the broader quality of implementation discussion in JDK 24.

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PR Comment: https://git.openjdk.org/jdk/pull/20063#issuecomment-2219563751