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Getting the Indices of a Matching Group in a Regular Expression

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Here, in this section, you will find the lower and upper indices of the matching group of the text through the regular expression in Java. This section explains some method or APIs which have been used in the following program.

Getting the Indices of a Matching Group in a Regular Expression

     

Here, in this section, you will find the lower and upper indices of the matching group of the text  through the regular expression in Java. This section explains some method or APIs which have been used in the following program.

Code Description:

Matcher.groupCount():
This method counts the matched string or text of the given group of the text or string.

Matcher.start(index):
Above method returns the starting index of the matching word.

Matcher.end(index):
This method returns the last position of the matching word.

String.subSequence(groupStart, groupEnd):
This method returns the character sequences from the given start index to the given end index of the string or text.

Here is the code of the program:

import java.util.regex.*;
import java.io.*;

public class IndicesOfGroupOfText{
  public static void main(String[] args){
  CharSequence inputStr = "abbabcd";
  String patternStr = "(a(b*))+(c*)";
  
  // Compile and use regular expression
  Pattern pattern = Pattern.compile(patternStr);
  Matcher matcher = pattern.matcher(inputStr);
  boolean matchFound = matcher.find();
  System.out.println("Complete string/text: " + inputStr);
  int a = 0;
  if(matchFound){
  // Get all groups for this match
  for(int i=0; i<=matcher.groupCount(); i++){
  a = a + 1;
  // Get the group's captured text
  String groupStr = matcher.group(i);
  System.out.println(groupStr);
  
  // Get the group's indices
  int groupStart = matcher.start(i);
  int groupEnd = matcher.end(i);
  System.out.println("Last index of the group of \'" 

+ groupStr + "\': " + groupStart + " " (groupEnd-1));
  
  // groupStr is equivalent to
  inputStr.subSequence(groupStart, groupEnd);
  }
  }
  if (a == 0){
  System.out.println("No match found.");
  System.exit(0);
  }
  }
}

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Posted on: February 22, 2008

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