[10] RFR 8134512 : provide Alpha-Numeric (logical) Comparator

Ivan Gerasimov ivan.gerasimov at oracle.com
Sun Aug 27 20:38:35 UTC 2017

Hello everyone!

Here's another iteration of the comparator with suggested improvements.

Now, there is the only input argument -- the alpha-comparator for 
comparing the non-decimal-digit sub-sequences.

For the javadoc I used the text suggested by Peter with some 
modifications, additional example and API/implementation notes. Overall, 
the javadoc looks heavier than need to me, so I'd love to hear comments 
about how to make it shorter and cleaner.

Also, I adopted the name AlphaDecimal, suggested by Peter.  This name is 
one of popular in the list of variants found in the wild. So, there are 
higher chances the users can find the routine by its name.

For testing if a code point is a decimal digit, I used 
(Character.getType(cp) == Character.DECIMAL_DIGIT_NUMBER), which seem to 
be more appropriate than Character.isDigit().  (The later is true for 
things like a digit in a circle, superscript, etc., which do not seem to 
be a part of a decimal number composed of several digits.)

The updated webrev:

Please review at your convenience.

With kind regards,

On 8/9/17 4:59 PM, Stuart Marks wrote:
> On 8/1/17 11:56 PM, Ivan Gerasimov wrote:
>> I've tried to go one step further and created even more abstract 
>> comparator:  It
>> uses a supplied predicate to decompose the input sequences into odd/even
>> subsequences (e.g. alpha/numeric) and then uses two separate 
>> comparator to
>> compare them. Additionally, a comparator for comparing sequences, 
>> consisting
>> only of digits is provided. For example, to build a case-insensitive
>> AlphaDecimal comparator one could use: 1) Character::isDigit -- as 
>> the predicate
>> for decomposing, 2) String::compareToIgnoreCase -- to compare alpha 
>> (i.e. odd
>> parts); to work with CharSequences one would need to make it
>> Comparator.comparing(CharSequence::toString, 
>> String::compareToIgnoreCase), 3)
>> The special decimal-only comparator, which compares the decimal 
>> representation
>> of the sequences. Here's the file with all the comparators and a 
>> simple test:
>> http://cr.openjdk.java.net/~igerasim/8134512/test/Test.java
> Hi, a couple follow-up thoughts on this.
> 1) Supplementary characters
> The current code uses Character.isDigit(char), which works only for 
> char values in the BMP (basic multilingual plane, values <= U+FFFF). 
> It won't work for supplementary characters. There are several blocks 
> of digits in the BMP, but there are several more in the supplementary 
> character range.
> I don't see any reason not to handle the supplementary characters as 
> well, except that it spoils the nice char-by-char technique of 
> processing the string. Instead, it'd have to pull in code point 
> values, which might be comprised of two surrogate chars. There are a 
> variety of methods on Character that help with this. Note that there 
> is an overload Character.isDigit(int) which takes any code point 
> value, including supplementary characters.
> 2) Too much generality?
> This version includes Predicate<Character> for determining whether a 
> character is part of the alphabetic or decimal portion of the string. 
> I'm thinking this might be overkill. It might be sufficient to 
> "hardwire" the partitioning predicate to be Character::isDigit and the 
> value mapping function to use Character::digit.
> The problem is that adding a predicate opens the door to a lot more 
> complexity, while providing dimishing value. First, the predicate 
> would have to handle code points (per the above) so it'd need to be an 
> IntPredicate. Second, there would also need to be a mapping function 
> from the code point value to a numeric value. This might be an 
> IntUnaryOperator. This would allow someone to sort based on Roman 
> numerals, using Character::getNumericValue. (Yes, Roman numerals are 
> in Unicode.) Or maybe the mapping function should return any 
> Comparable value, not an int. ... See where I'm going here?
> Since this kind of sorting is intended to be viewed by people, it's 
> probably worth providing full internationalization support 
> (supplementary characters, and delegation to sub-comparators, to allow 
> locale-specific collating sequences). But I start to question any 
> complexity beyond that.
> s'marks

With kind regards,
Ivan Gerasimov

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