Java/Regular Expressions/Group

Capturing Text in a Group in a Regular Expression

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   CharSequence inputStr = "abbabcd";
   String patternStr = "(a(b*))+(c*)";
   // Compile and use regular expression
   Pattern pattern = Pattern.rupile(patternStr);
   Matcher matcher = pattern.matcher(inputStr);
   boolean matchFound = matcher.find();
   if (matchFound) {
     // Get all groups for this match
     for (int i = 0; i <= matcher.groupCount(); i++) {
       String groupStr = matcher.group(i);
     }
   }
 }

}

</source>
   
  
 
  

Find group number 1 of the second find

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   Pattern p = Pattern.rupile("t(est)");
   String candidateString = "This is a test. This is a test.";
   Matcher matcher = p.matcher(candidateString);
   matcher.find();
   String group_0 = matcher.group(0);
   String group_1 = matcher.group(1);
   System.out.println("Group 0 " + group_0);
   System.out.println("Group 1 " + group_1);
 }

}

</source>
   
  
 
  

find the starting point of the first subgroup

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("t(est)");
   String candidateString = "This is a test. This is another test.";
   Matcher matcher = p.matcher(candidateString);
   int nextIndex = matcher.start(1);
   System.out.println(candidateString);
   System.out.println(nextIndex);
 }

}

</source>
   
  
 
  

Find the starting point of the second subgroup

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("t(est)");
   String candidateString = "This is a test. This is another test.";
   Matcher matcher = p.matcher(candidateString);
   matcher.find();
   int startIndex = matcher.start(0);
   System.out.println(candidateString);
   System.out.println(startIndex);
 }

}

</source>
   
  
 
  

Getting the Indices of a Matching Group in a Regular Expression

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   CharSequence inputStr = "abbabcd";
   String patternStr = "(a(b*))+(c*)";
   Pattern pattern = Pattern.rupile(patternStr);
   Matcher matcher = pattern.matcher(inputStr);
   boolean matchFound = matcher.find();
   if (matchFound) {
     // Get all groups for this match
     for (int i = 0; i <= matcher.groupCount(); i++) {
       // Get the group"s captured text
       String groupStr = matcher.group(i);
       // Get the group"s indices
       int groupStart = matcher.start(i);
       int groupEnd = matcher.end(i);
       // groupStr is equivalent to
       inputStr.subSequence(groupStart, groupEnd);
     }
   }
 }

}

</source>
   
  
 
  

Matcher.group(int) Method Example

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("t(est)");
   String candidateString = "This is a test. This is another test.";
   Matcher matcher = p.matcher(candidateString);
   // Find group number 0 of the first find
   matcher.find();
   String group_0 = matcher.group(0);
   String group_1 = matcher.group(1);
   System.out.println("Group 0 " + group_0);
   System.out.println("Group 1 " + group_1);
   System.out.println(candidateString);
 }

}

</source>
   
  
 
  

Using a Non-Capturing Group in a Regular Expression

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   String inputStr = "abbabcd";
   String patternStr = "(a(?:b*))+(c*)";
   // (?:b*) is a non-capturing group
   Pattern pattern = Pattern.rupile(patternStr);
   Matcher matcher = pattern.matcher(inputStr);
   boolean matchFound = matcher.find();
   if (matchFound) {
     for (int i = 0; i <= matcher.groupCount(); i++) {
       String groupStr = matcher.group(i);
     }
   }
 }

}

</source>
   
  
 
  

Using appendReplacement with Subgroup Replacements

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("(another) (test)");
   StringBuffer sb = new StringBuffer();
   String candidateString = "This is another test.";
   String replacement = "$1 AAA $2";
   Matcher matcher = p.matcher(candidateString);
   matcher.find();
   matcher.appendReplacement(sb, replacement);
   String msg = sb.toString();
   System.out.println(msg);
 }

}

</source>
   
  
 
  

Using the Captured Text of a Group within a Pattern

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   String patternStr = "<(\\S+?).*?>(.*?)</\\1>";
   Pattern pattern = Pattern.rupile(patternStr);
   Matcher matcher = pattern.matcher("");
   // Set the input
   matcher.reset("xx <tag a=b> yy </tag> zz");
   // Get tagname and contents of tag
   boolean matchFound = matcher.find(); 
   String tagname = matcher.group(1); 
   String contents = matcher.group(2); 
   matcher.reset("xx <tag> yy </tag0>");
   matchFound = matcher.find(); 
 }

}

</source>
   
  
 
  

Using the Captured Text of a Group within a Replacement Pattern

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String[] argv) throws Exception {
   String patternStr = "\\((\\w+)\\)";
   String replaceStr = "<$1>";
   Pattern pattern = Pattern.rupile(patternStr);
   CharSequence inputStr = "a (b c) d (ef) g";
   Matcher matcher = pattern.matcher(inputStr);
   String output = matcher.replaceAll(replaceStr);
 }

}

</source>
   
  
 
  

Working with Groups: characters and digits

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("\\w\\d");
   String candidate = "AAA C1 ";
   Matcher matcher = p.matcher(candidate);
   if (matcher.find()) {
     String tmp = matcher.group(0);
     System.out.println(tmp);
   }
 }

}

</source>
   
  
 
  

Working with Subgroups

   <source lang="java">

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Main {

 public static void main(String args[]) {
   Pattern p = Pattern.rupile("\\w(\\d)");
   String candidate = "w5 ";
   Matcher matcher = p.matcher(candidate);
   if (matcher.find()) {
     String tmp = matcher.group(0);
     System.out.println(tmp); 
     tmp = matcher.group(1); 
     System.out.println(tmp);
   }
 }

}

</source>