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

[Roger Riggs]

On Fri, 16 Oct 2020 13:10:24 GMT, Chris Hegarty <chegar 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);
>      }
> ```

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.

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