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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: Tue, 27 Mar 2012 23:27:58 +0200
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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
>> {
>>    public static void split
>>    ( final java.lang.String text )
>>    { java.util.regex.Pattern pattern =
>>      java.util.regex.Pattern.compile
>>      ( ".*?(?:am|pm),?", java.util.regex.Pattern.CASE_INSENSITIVE );
>>      java.util.regex.Matcher matcher = pattern.matcher( text );
>>      while( matcher.find() )
>>      java.lang.System.out.println( matcher.group( 0 )); }
>>
>>    public static void main( final java.lang.String[] args )
>>    { split( "Fri 7:30 PM, Sat 2 PM, Sun 2:30 PM" ); }}
>
> 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.*?(?:am|pm))(?:,\\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 might even sneak a "\\s*" in between "pm)" and "(?:," to even catch 
cases where there are spaces before the separator.

Kind regards

	robert