RFR: 8251989: Hex formatting and parsing utility

[Roger Riggs]

On Fri, 2 Oct 2020 18:14:32 GMT, Weijun Wang <weijun at openjdk.org> wrote:

>> java.util.HexFormat utility:
>> 
>>  - Format and parse hexadecimal strings, with parameters for delimiter, prefix, suffix and upper/lowercase
>>  - Static factories and builder methods to create HexFormat copies with modified parameters.
>>  - Consistent naming of methods for conversion of byte arrays to formatted strings and back: formatHex and parseHex
>>  - Consistent naming of methods for conversion of primitive types: toHexDigits... and fromHexDigits...
>>  - Prefix and suffixes now apply to each formatted value, not the string as a whole
>>  - Using java.util.Appendable as a target for buffered conversions so output to Writers and PrintStreams
>>    like System.out are supported in addition to StringBuilder. (IOExceptions are converted to unchecked exceptions)
>>  - Immutable and thread safe, a "value-based" class
>> 
>> See the [HexFormat
>> javadoc](http://cr.openjdk.java.net/~rriggs/8251989-hex-formatter/java.base/java/util/HexFormat.html) for details.
>> Review comments and suggestions welcome.
>
> src/java.base/share/classes/java/util/HexFormat.java line 290:
> 
>> 288:      * @return returns {@code true} if the hexadecimal digits will be uppercase,
>> 289:      *          otherwise {@code false}
>> 290:      */
> 
> Can someone choose their own `digits`? If not, how about "=="?

I don't think it would be called HexFormat doing Hexadecimal conversions if it could be an arbitrary set of digits.
The Arrays.equals implementation contains the == test so its implementers choice.

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