JDK 13 RFR of JDK-8223112: Clarify operational semantics of java.util.Objects.equals()

[Joseph D. Darcy]

PS Please also review the CSR

     https://bugs.openjdk.java.net/browse/JDK-8223265

Note that the particular implementation used in Objects.equals was 
recommended in its initial code review back in 2009:

http://mail.openjdk.java.net/pipermail/core-libs-dev/2009-September/002580.html

Thanks,

-Joe

On 5/2/2019 2:42 PM, Joe Darcy wrote:
> Hello,
>
> Bug JDK-8223112 notes indirectly that if Objects.equals is called with 
> (foo, null) and foo has a buggy equals method that returns true for 
> null, the wrong result will be computed.
>
> I don't think code should be added to Objects.equals itself to guard 
> against this case. Instead, I think the operational semantics of the 
> implementation should be made explicit in the specification.
>
> Please review the patch below.
>
> Thanks,
>
> -Joe
>
> diff -r 7ab4310ed472 src/java.base/share/classes/java/util/Objects.java
> --- a/src/java.base/share/classes/java/util/Objects.java    Wed May 01 
> 20:25:31 2019 -0700
> +++ b/src/java.base/share/classes/java/util/Objects.java    Thu May 02 
> 14:41:06 2019 -0700
> @@ -62,10 +62,11 @@
>       * Returns {@code true} if the arguments are equal to each other
>       * and {@code false} otherwise.
>       * Consequently, if both arguments are {@code null}, {@code true}
> -     * is returned and if exactly one argument is {@code null}, {@code
> -     * false} is returned.  Otherwise, equality is determined by using
> -     * the {@link Object#equals equals} method of the first
> -     * argument.
> +     * is returned.  Otherwise, if the first argument is not {@code
> +     * null}, equality is determined by calling the {@link
> +     * Object#equals equals} method of the first argument with the
> +     * second argument of this method. Otherwise, {@code false} is
> +     * returned.
>       *
>       * @param a an object
>       * @param b an object to be compared with {@code a} for equality
>
> ...
>
>     public static boolean equals(Object a, Object b) {
>         return (a == b) || (a != null && a.equals(b));
>     }
>