Get the index of a pattern in a string using regex

Question

I want to search a string for a specific pattern.

Do the regular expression classes provide the positions (indexes within the string) of the pattern within the string?
There can be more that 1 occurences of the pattern.
Any practical example?

docs.oracle.com/javase/6/docs/api/java/util/regex/Matcher.html — JB Nizet
– JB Nizet, Commented Jan 20, 2012 at 8:24

Jean Logeart · Accepted Answer · 2012-01-20 08:59:51Z

206

Use Matcher:

public static void printMatches(String text, String regex) {
    Pattern pattern = Pattern.compile(regex);
    Matcher matcher = pattern.matcher(text);
    // Check all occurrences
    while (matcher.find()) {
        System.out.print("Start index: " + matcher.start());
        System.out.print(" End index: " + matcher.end());
        System.out.println(" Found: " + matcher.group());
    }
}

edited Jan 20, 2012 at 8:59

answered Jan 20, 2012 at 8:23

Jean Logeart

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Comments

Ar maj · Accepted Answer · 2017-06-01 20:56:11Z

6

special edition answer from Jean Logeart

public static int[] regExIndex(String pattern, String text, Integer fromIndex){
    Matcher matcher = Pattern.compile(pattern).matcher(text);
    if ( ( fromIndex != null && matcher.find(fromIndex) ) || matcher.find()) {
        return new int[]{matcher.start(), matcher.end()};
    }
    return new int[]{-1, -1};
}

answered Jun 1, 2017 at 20:56

Ar maj

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Comments

Shadow · Accepted Answer · 2012-01-20 08:24:26Z

-3

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");
      }
   }
}

Result

Found value: This order was places for QT3000! OK?
Found value: This order was places for QT300
Found value: 0

answered Jan 20, 2012 at 8:24

Shadow

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4 Comments

El Ronnoco Over a year ago

Please comment when downvoting! @Shadow I assume this has been downvoted as it does not, as the OP request, give the index of the match...

user684934 Over a year ago

Okay... I downvoted because this answer does not address the question.

Alan Moore Over a year ago

Your regex is faulty, too. The first (.*) originally consumes the whole string, then it backs off just far enough to let (\d+) match one digit, leaving then the second (.*) to consume whatever's left. Not a particularly useful result, I'd say. Oh, and you left group(3) out of your results.

mez.pahlan Over a year ago

Doesn't give the index

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