Matcher group(int) method in Java with Examples

The group(int group) method of Matcher Class is used to get the group index of the match result already done, from the specified group.

Syntax:

public String group(int group)

Parameters: This method takes a parameter group which is the group from which the group index of the matched pattern is required.

Return Value: This method returns the index of the first character matched from the specified group.

Exception: This method throws:

• IllegalStateException if no match has yet been attempted, or if the previous match operation failed.
• IndexOutOfBoundsException if there is no capturing group in the pattern with the given index.

Below examples illustrate the Matcher.group() method:

Example 1:

// Java code to illustrate group() method

import java.util.regex.*;

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

        // Get the regex to be checked
        String regex = "(G*s)";

        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);

        // Get the String to be matched
        String stringToBeMatched
            = "GeeksForGeeks";

        // Create a matcher for the input String
        Matcher matcher
            = pattern
                  .matcher(stringToBeMatched);

        // Get the current matcher state
        MatchResult result
            = matcher.toMatchResult();
        System.out.println("Current Matcher: "
                           + result);

        while (matcher.find()) {
            // Get the group matched using group() method
            System.out.println(matcher.group(1));
        }
    }
}

Output:

Current Matcher: java.util.regex.Matcher[pattern=(G*s) region=0,13 lastmatch=]
s
s

Example 2:

// Java code to illustrate group() method

import java.util.regex.*;

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

        // Get the regex to be checked
        String regex = "(G*G)";

        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);

        // Get the String to be matched
        String stringToBeMatched
            = "GFGFGFGFGFGFGFGFGFG";

        // Create a matcher for the input String
        Matcher matcher
            = pattern
                  .matcher(stringToBeMatched);

        // Get the current matcher state
        MatchResult result
            = matcher.toMatchResult();
        System.out.println("Current Matcher: "
                           + result);

        while (matcher.find()) {
            // Get the group matched using group() method
            System.out.println(matcher.group(0));
        }
    }
}

Output:

Current Matcher: java.util.regex.Matcher[pattern=(G*G) region=0,19 lastmatch=]
G
G
G
G
G
G
G
G
G
G

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/regex/Matcher.html#group-int-