RFR: 8251989: Hex formatting and parsing utility [v4]

[Roger Riggs]

On Fri, 16 Oct 2020 14:00:38 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Maybe I'm being too pedantic, but is the use of the term _copy_ for the withers overly prescriptive, and possibly
>> limiting an implementation? For example, for `withDelimiter` does _copy_ preclude such an implementation:
>>      /**
>>       * Returns a copy of this {@code HexFormat} with the delimiter.
>>       * @param delimiter the delimiter, non-null, may be empty
>>       * @return a copy of this {@code HexFormat} with the delimiter
>>       */
>>      public HexFormat withDelimiter(String delimiter) {
>> +        if (delimiter.equals(this.delimiter))
>> +            return this;
>>          return new HexFormat(delimiter, this.prefix, this.suffix, this.digits);
>>      }
>
>> Maybe I'm being too pedantic, but is the use of the term _copy_ for the withers overly prescriptive, and possibly
>> limiting an implementation? For example, for `withDelimiter` does _copy_ preclude such an implementation:
>> ```
>>      /**
>>       * Returns a copy of this {@code HexFormat} with the delimiter.
>>       * @param delimiter the delimiter, non-null, may be empty
>>       * @return a copy of this {@code HexFormat} with the delimiter
>>       */
>>      public HexFormat withDelimiter(String delimiter) {
>> +        if (delimiter.equals(this.delimiter))
>> +            return this;
>>          return new HexFormat(delimiter, this.prefix, this.suffix, this.digits);
>>      }
>> ```
> 
> Since the instances are immutable, it seemed useful to emphasize that only the instance returned has the requested
> change.  Discarding the return value was incorrect programming.  The original instance is not modified. The "copy"
> phrasing was used throughout java.time. Since reference equality is specifically dis-allowed for value-based objects,
> there is no way to discover a difference between a copy and the original with the same parameters.

Thanks for the PR.
For TestNG asserts as a point of personal style, I eschew the static imports for asserts.
The correction for `<A extends Appendable>` is already in the works.

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PR: https://git.openjdk.java.net/jdk/pull/482