RFR: 8251989: Hex formatting and parsing utility

[Weijun Wang]

On Fri, 2 Oct 2020 15:18:04 GMT, Roger Riggs <rriggs 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.

The class name already has `Hex` inside, and methods names still contain it. Also, I found it unexpected that
`fromHexDigits` returns an integer. Can we use `encode`, `decode`, `decodeInt`, `decodeLong` etc?

src/java.base/share/classes/java/util/HexFormat.java line 213:

> 211:      * @param delimiter the {@code delimiter}, non-null, may be empty
> 212:      * @return a copy of this {@code HexFormat} with the {@code delimiter}
> 213:      */

Is this very useful now that we already have `ofDelimeter(String)`?

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 "=="?

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