RFR: 8274528: Add comment to explain an HKDF optimization in SSLSecretDerivation

[Jamil Nimeh]

On Thu, 30 Sep 2021 14:15:59 GMT, Bradford Wetmore <wetmore at openjdk.org> wrote:

>> src/java.base/share/classes/sun/security/ssl/SSLSecretDerivation.java line 153:
>> 
>>> 151:         private final byte[] label;
>>> 152: 
>>> 153:         SecretSchedule(String label) {
>> 
>> Why are we opening the visibility on this enum?  As far as I can tell it is only ever referenced within the SSLSecretDerivation class and could remain private if it hasn't been causing any problems up to now.
>
> From the JLS §8.8.3:  https://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.8.3
> 
> `
> If no access modifier is specified for the constructor of an enum type, the constructor is private. 
> '
> 
> It's kind of like adding 'public' to interfaces.  They're not necessary.
> 
> Does that alleviate your concern?

Yes it does.  I forgot that enums are private when there's no visibility explicitly stated.  So given that the whole thing looks good to me.

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PR: https://git.openjdk.java.net/jdk/pull/5765