Confused on the Topic of Capturing Groups?

Question

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

public class RegexMatches
{
    public static void main( String args[] ){

      // String to be scanned to find the pattern.
      String line = "This order was places for QT3000! OK?";
      String pattern = "(.*)(\\d+)(.*)";

      // Create a Pattern object
      Pattern r = Pattern.compile(pattern);

      // Now create matcher object.
      Matcher m = r.matcher(line);
      if (m.find( )) {
         System.out.println("Found value: " + m.group(0) );
         System.out.println("Found value: " + m.group(1) );
         System.out.println("Found value: " + m.group(2) );
      } else {
         System.out.println("NO MATCH");
      }
   }
}

I want to knew how the Pattern and Matcher object works ?

I reffered few examples but i cant come up with that.

what does the pattern does and what does the Matcher do..How wil the find and group work. — 09Q71AO534, Aug 01 '13 at 09:36
The groups are numbered from **1**, `m.group() == m.group(0)` is the entire match of all. `.find()` is for (repeated) searches, `.matches()` for a single match for the entire string. — Joop Eggen, Aug 01 '13 at 09:37
What does the group(\\d+) do..which pattern will it look for.. — 09Q71AO534, Aug 01 '13 at 09:39
possible duplicate of [A Java regular expression about finding digit string](http://stackoverflow.com/questions/11434913/a-java-regular-expression-about-finding-digit-string) and also: http://stackoverflow.com/questions/17969436/java-regex-capturing-groups — assylias, Aug 01 '13 at 09:39
One or more (postfix `+`) of a digit `\d`. See [Pattern](http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html) — Joop Eggen, Aug 01 '13 at 09:40

score 1 · Answer 1 · answered Aug 01 '13 at 10:02

1

Your groups start from index = 1. Zero is an index for a whole match.

So, the first (.*) is in m.group(1), (\\\d+) is in m.group(2), and the second (.*) is in m.group(3)

answered Aug 01 '13 at 10:02

James Joomer

41
2

score 0 · Answer 2 · answered Aug 01 '13 at 10:27

0

http://www.regular-expressions.info/tutorial.html contains pretty much everything you need to know about regular expressions

answered Aug 01 '13 at 10:27

RokL

2,663
3
22
26

Confused on the Topic of Capturing Groups?

2 Answers2