Java Regex: matches(pattern, value) returns true but group() fails to match

Question

I have an odd problem with a regular expression in Java. I tested my Regex and my value here and it works. It says there are 3 groups (correct) the match for the first group

Answer 1

You need to call find() before group():

String pattern = "([^-]*)-([\\D]*)([\\d]*)"; 
String value = "SSS-BB0000";
Matcher matcher = Pattern.compile(pattern).matcher(value); 
if (matcher.find()) {
  System.out.println(matcher.group()); // SSS-BB0000
  System.out.println(matcher.group(0)); // SSS-BB0000
  System.out.println(matcher.group(1)); // SSS
  System.out.println(matcher.group(2)); // BB
  System.out.println(matcher.group(3)); // 0000
}

When you invoke matcher(value), you are merely creating a Matcher object that will be able to match your value. In order to actually scan the input, you need to use find() or lookingAt():

References:

• Matcher#find()

Answer 2

I faced the same issue. Was calling matcher.group(1) WITHOUT checking matcher.find(). Adding if check for matcher.find() solved the problem.