Matcher start() method in Java with Examples

The start() method of Matcher Class is used to get the start index of the match result already done.

Syntax:

public int start()

Parameters: This method do not takes any parameter.

Return Value: This method returns the index of the first character matched.0

Exception: This method throws IllegalStateException if no match has yet been attempted, or if the previous match operation failed.

Below examples illustrate the Matcher.start() method:

Example 1:

// Java code to illustrate start() method

import java.util.regex.*;

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

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

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

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

        // 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 first index of match result
            System.out.println(matcher.start());
        }
    }
}

Output:

Current Matcher: java.util.regex.Matcher[pattern=(G*k) region=0,5 lastmatch=]
3

Example 2:

// Java code to illustrate start() 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 = "GFG";

        // 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 first index of match result
            System.out.println(matcher.start());
        }
    }
}

Output:

Current Matcher: java.util.regex.Matcher[pattern=(G*G) region=0,3 lastmatch=]
0
2

Reference: Oracle Doc