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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Keeping the split token in a Java regular expression
Date: Wed, 28 Mar 2012 07:28:13 +0200
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On 03/27/2012 11:27 PM, Robert Klemme wrote:
> On 03/27/2012 01:26 AM, Lew wrote:
>> Stefan Ram wrote:
>>> laredotornado writes:
>>>> What I would like to do is split the expression wherever I have an
>>>
>>> public class Main
...
>>
>> This excellent (except for layout) example deserves to be archived.
>
> What do you find excellent about this? I find it has some deficiencies
>
> - the separator is included in the match (which goes against the
> requirements despite the thread subject)
> - spaces after a separator comma are included in the next token as
> leading text
> - the method really does more than splitting (namely printing), so the
> name does not reflect what's going on
> - the Pattern is compiled on _every_ invocation of the method
> - the method is unnecessary restricted, argument type CharSequence is
> sufficient
>
> Test output for
> "Fri 7:30 PM, Sat 2 PM, Sun 2:30 PM"
> "Fri 8 PM, Sat 1, 3, and 5 PM"
>
> Fri 7:30 PM,
> Sat 2 PM,
> Sun 2:30 PM
> ---
> Fri 8 PM,
> Sat 1, 3, and 5 PM
> ---
>
> I would change that to

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
     private static final Pattern SPLIT_PATTERN = Pattern.compile(
             "(\\S.*?[ap]m)(?:,\\s*)?", Pattern.CASE_INSENSITIVE);

     public static void splitPrint(final CharSequence text) {
         for (final Matcher m = SPLIT_PATTERN.matcher(text); m.find();) {
             System.out.println(m.group(1));
         }
     }

     public static List<String> split(final CharSequence text) {
         final List<String> result = new ArrayList<String>();

         for (final Matcher m = SPLIT_PATTERN.matcher(text); m.find();) {
             result.add(m.group(1));
         }

         return result;
     }

     public static void main(final java.lang.String[] args) {
         splitPrint("Fri 7:30 PM, Sat 2 PM, Sun 2:30 PM");
         System.out.println("---");
         splitPrint("Fri 8 PM, Sat 1, 3, and 5 PM");
         System.out.println("---");
     }
}

I had overlooked a fairly obvious improvement with regards to am/pm parsing.

> I might even sneak a "\\s*" in between "pm)" and "(?:," to even catch
> cases where there are spaces before the separator.

Kind regards

	robert