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Non capturing groups Java regular expressions:
Using capturing groups you can treat multiple characters as a single unit. You just need to place the characters to be grouped inside a set of parentheses. For example −
(.*)(\d+)(.*)
If you are trying to match multiple groups the match results of each group is captured. You can get the results a group by passing its respective group number to the group() method. 1,2, 3 etc.. (from right to left) group 0 indicates the whole match.
Example
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class CapturingGroups {
public static void main( String args[] ) {
System.out.println("Enter input text");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String regex = "(.*)(\d+)(.*)";
//Create a Pattern object
Pattern pattern = Pattern.compile(regex);
//Now create matcher object.
Matcher matcher = pattern.matcher(input);
if (matcher.find( )) {
System.out.println("Found value: " + matcher.group(0) );
System.out.println("Found value: " + matcher.group(1) );
System.out.println("Found value: " + matcher.group(2) );
System.out.println("Found value: " + matcher.group(3) );
} else {
System.out.println("NO MATCH");
}
}
}Output
Enter input text sample data with 1234 (digits) in middle Found value: sample data with 1234 (digits) in middle Found value: sample data with 123 Found value: 4 Found value: (digits) in middle
Non capturing groups
The non-capturing group provides the same functionality of a capturing group but it does not captures the result
For example, if you need to match a URL or a phone number from a text using groups, since the starting part of the desired sub strings is same you need not capture the results of certain groups in such cases you can use non capturing groups. A non-capturing group starts with (?: and ends with ).
Example
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class CapturingGroups {
public static void main( String args[] ) {
System.out.println("Enter input text");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String regex = "(.*)(?:\d+)(.*)";
//Create a Pattern object
Pattern pattern = Pattern.compile(regex);
//Now create matcher object.
Matcher matcher = pattern.matcher(input);
if (matcher.find( )) {
System.out.println("Found value: " + matcher.group(0) );
System.out.println("Found value: " + matcher.group(1) );
System.out.println("Found value: " + matcher.group(2) );
} else {
System.out.println("NO MATCH");
}
}
}Output
Enter input text sample data with 1234 (digits) in middle Found value: sample data with 1234 (digits) in middle Found value: sample data with 123 Found value: (digits) in middle
Note: The non-capturing group will not be included in the group count.
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