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Groups > comp.lang.java.programmer > #2885

Re: regex capability

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On 5 Apr., 14:28, Patricia Shanahan <p...@acm.org> wrote:
> On 4/5/2011 2:10 AM, Paul Cager wrote:
>
> > On Apr 5, 2:35 am, markspace<-@.>  wrote:
> >> On 4/4/2011 1:13 PM, Robert Klemme wrote:
>
> >>> if ( m.matches() ) {
> >>> for (m = number.matcher(m.group(1)); m.find();) {
> >>> int x = Integer.parse(m.group());
> >>> }
>
> >> Why re-invent the wheel?

In this case I just wanted to demonstrate the strategy to first check
overall validity of the input and extract the interesting part and
then ripping that interesting part apart.  Whether a Scanner or
another Matcher is used for the second step wasn't that important to
me.  Also, the thread is called "regex capability". :-)

But, of course, your approach using the Scanner is perfectly
compatible with the two step strategy as Patricia also pointed
out. :-)

> >> public class ScannerTest {
> >>       public static void main(String[] args) {
> >>           StringReader in = new StringReader(
> >>                   "Support DDR2 100/200/300/400 DDR2 SDRAM");
>
> >>           Scanner scanner = new Scanner(in);
> >>           scanner.useDelimiter( "[^0-9]+" );
> >>           while( scanner.hasNextInt() ) {
> >>               System.out.println( scanner.nextInt() );
> >>           }
> >>       }
>
> >> }
>
> >> (Lightly tested.)
>
> > $ java ScannerTest
> > 2
> > 100
> > 200
> > 300
> > 400
> > 2
>
> This is a nice illustration of the case for a strategy I often use in
> this sort of situation, combining tools using each to do the jobs it
> does best.
>
> For example, a regular expression match could pull out the
> "100/200/300/400" substring, and a Scanner could extract the integers
> from that. More generally, it could be split and then each of the split
> results processed some other way.

I generally prefer scanning over splitting in those cases.  The
difference might be negligible for this case but assuming that the
original pattern changes (e.g. because we want to allow "@" as
separator instead of or additionally to "/") then for the split
approach two patterns need to be changed while for scanning of
integers (pattern \d+) only the master pattern needs to change.  Also,
with scanning it is clear what I want (positively defining the matched
portion) while with splitting it is not so clear (negatively defining
what I do not want, the separator) - but that leaves a lot of room for
what is returned from _between_ separators.

Kind regards

robert

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regex capability Roedy Green <see_website@mindprod.com.invalid> - 2011-04-04 00:19 -0700
  Re: regex capability Leif Roar Moldskred <leifm@dimnakorr.com> - 2011-04-04 02:34 -0500
    Re: regex capability Roedy Green <see_website@mindprod.com.invalid> - 2011-04-04 00:50 -0700
      Re: regex capability Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-04-04 08:03 -0400
        Re: regex capability Patricia Shanahan <pats@acm.org> - 2011-04-04 05:25 -0700
        Re: regex capability David Lamb <dalamb@cs.queensu.ca> - 2011-04-04 18:51 -0400
      Re: regex capability Jim Gibson <jimsgibson@gmail.com> - 2011-04-04 17:07 -0700
  Re: regex capability bugbear <bugbear@trim_papermule.co.uk_trim> - 2011-04-04 09:26 +0100
    Re: regex capability Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-04-04 19:20 +0200
    Re: regex capability Robert Klemme <shortcutter@googlemail.com> - 2011-04-04 22:13 +0200
      Re: regex capability markspace <-@.> - 2011-04-04 18:35 -0700
        Re: regex capability bugbear <bugbear@trim_papermule.co.uk_trim> - 2011-04-05 09:09 +0100
        Re: regex capability Paul Cager <paul.cager@googlemail.com> - 2011-04-05 02:10 -0700
          Re: regex capability Patricia Shanahan <pats@acm.org> - 2011-04-05 05:28 -0700
            Re: regex capability Robert Klemme <shortcutter@googlemail.com> - 2011-04-05 06:33 -0700
              Re: regex capability markspace <-@.> - 2011-04-05 10:07 -0700

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