Question

I have following lines of code

String time = "14:35:59.99";
String timeRegex = "(([01][0-9])|(2[0-3])):([0-5][0-9]):([0-5][0-9])(.([0-9]{1,3}))?";
String hours, minutes, seconds, milliSeconds;
Pattern pattern = Pattern.compile(timeRegex);
Matcher matcher = pattern.matcher(time);
if (matcher.matches()) {
    hours = matcher.replaceAll("$1");
    minutes = matcher.replaceAll("$4");
    seconds = matcher.replaceAll("$5");
    milliSeconds = matcher.replaceAll("$7");
}

I am getting hours, minutes, seconds, and milliSeconds using the matcher.replace method and back references of regex groups. Is there any better method to get value of regex groups. I tried

hours = matcher.group(1);

but it throws the following exception:

java.lang.IllegalStateException: No match found
    at java.util.regex.Matcher.group(Matcher.java:477)
    at com.abnamro.cil.test.TimeRegex.main(TimeRegex.java:70)

Am I missing something here?

Answer 1

It works fine if you avoid calling matcher.replaceAll. When you call replaceAll it forgets any previous matches.

String time = "14:35:59.99";
String timeRegex = "([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9])(?:\\.([0-9]{1,3}))?";
Pattern pattern = Pattern.compile(timeRegex);
Matcher matcher = pattern.matcher(time);
if (matcher.matches()) {
    String hours = matcher.group(1);
    String minutes = matcher.group(2);
    String seconds = matcher.group(3);
    String miliSeconds = matcher.group(4);
    System.out.println(hours + ", " + minutes  + ", " + seconds + ", " + miliSeconds);
}

Notice that I’ve also made a couple of improvements to your regular expression:

• I’ve used non-capturing groups (?: ... ) for the groups that you aren’t interested in capturing.
• I’ve changed . which matches any character to \\. which matches only a dot.

See it working online: ideone