RFR: 8251989: Hex formatting and parsing utility [v10]

[Roger Riggs]

On Fri, 27 Nov 2020 09:54:07 GMT, Chris Hegarty <chegar at openjdk.org> wrote:

>> Roger Riggs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 19 additional commits since the last revision:
>> 
>>  - Clarified that suffix() and prefix() methods do not return null, instead the empty string is returned.
>>  - Merge branch 'master' into 8251989-hex-formatter
>>  - Merge branch 'master' into 8251989-hex-formatter
>>  - Merge branch 'master' into 8251989-hex-formatter
>>  - The HexFormat API indexing model for array and string ranges is changed
>>    to describe the range using 'fromIndex (inclusive)' and 'toIndex (exclusive)'.
>>    
>>    Initially, it was specified as 'index' and 'length'. However, both byte arrays
>>    and strings used in the HexFormat API typically use fromIndex and toIndex
>>    to describe ranges.  Using the same indexing model can prevent mistakes.
>>    
>>    The change affects the methods and corresponding tests:
>>    
>>        formatHex(byte[] bytes, int fromIndex, int toIndex)
>>        formatHex(A out, byte[] bytes, int fromIndex, int toIndex)
>>        parseHex(char[] chars, int fromIndex, int toIndex)
>>        parseHex(CharSequence string, int fromIndex, int toIndex)
>>        fromHexDigits(CharSequence string, int fromIndex, int toIndex)
>>        fromHexDigitsToLong(CharSequence string, int fromIndex, int toIndex)
>>  - - Added @see and @link references to Integer.toHexString and Long.toHexString
>>    - Clarified parsing is case insensistive in various parse and fromXXX methods
>>    - Source level cleanup based on review comments
>>    - Expanded some javadoc tag text to make it more descriptive
>>    - Consistent use of 'hexadecimal' vs 'hex'
>>  - Review comment updates to class javadoc
>>  - Review comment updates, in the example code, and to describe the characters used to convert to hexadecimal
>>  - Correct length of StringBuilder in formatHex;
>>    Correct bug in formatHex(char[], 2, 3) and add test for subranges of char[]
>>  - Merge branch 'master' into 8251989-hex-formatter
>>  - ... and 9 more: https://git.openjdk.java.net/jdk/compare/706644aa...b19d2827
>
> src/java.base/share/classes/java/util/HexFormat.java line 617:
> 
>> 615:      * Returns the two hexadecimal characters for the {@code byte} value.
>> 616:      * Each nibble (4 bits) from most significant to least significant of the value
>> 617:      * is formatted as if by {@link #toLowHexDigit(int) toLowHexDigit(nibble)}.
> 
> It might be more straightforward to frame this in terms of toLowHexDigit and toHighHexDigit (rather than only toLowHexDigit).  `nibble`- should the param name for to(Low|High)HexDigit be named `nibble` ?

The description as `from most to least significant` is used to be consistent across all of the `toHexDigits` methods regardless of whether the argument is a `byte`, `short`, `int`, or `long`.  

The `toLowDigit` and `toHighDigit` methods extract a nibble from the corresponding bits of the parameter value.  
The type of the argument is 'int' to make it easier to pass without needing to cast it to a byte.

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