The start(int group) method of Matcher Class is used to get the start index of the match result already done, from the specified group.
Syntax:
public int start(int group)
Parameters: This method takes a parameter group which is the group 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 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.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*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(1)); } }} |
Output:
Current Matcher: java.util.regex.Matcher[pattern=(G*s) region=0,13 lastmatch=]
4
12
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 = "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(0)); } }} |
Output:
Current Matcher: java.util.regex.Matcher[pattern=(G*G) region=0,19 lastmatch=]
0
2
4
6
8
10
12
14
16
18
Reference: Oracle Doc
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