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
