Matcher start(String) method in Java with Examples

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

Syntax:

public int start(String string)

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

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

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 name.

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 = "\\b(?<Geeks>[A-Za-z\\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 first index of match result 
            System.out.println(matcher.start("Geeks")); 
        } 
    } 
} 

Output:

Current Matcher: java.util.regex.Matcher[pattern=\b(?[A-Za-z\s]+) region=0,13 lastmatch=]
0

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 = "\\b(?<GFG>[A-Za-z\\s]+)"; 
  
        // 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 first index of match result 
            System.out.println(matcher.start("GFG")); 
        } 
    } 
} 

Output:

Current Matcher: java.util.regex.Matcher[pattern=\b(?[A-Za-z\s]+) region=0,22 lastmatch=]
3

Reference: Oracle Doc

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