Regex capture group within if statement in Java

Question

I'm facing a stupid problem... I know how to use Pattern and Matcher objects to capture a group in Java.

However, I cannot find a way to use them with an if statement where each choice depends on a match (simple example to illustrate the question, in reality, it's more complicated) :

String input="A=B";
String output="";

if (input.matches("#.*")) {
    output="comment";
} else if (input.matches("A=(\\w+)")) {
    output="value of key A is ..."; //how to get the content of capturing group?
} else { 
    output="unknown";
}

Should I create a Matcher for each possible test?!

} else if (input.matches("A=(\\w+)")) { output="value of key A is " + input.split("=")[1]; } — DevilsHnd - 退した
– DevilsHnd - 退した, Commented Jul 1, 2022 at 16:27
If you really want to use regexep you should probably use 1 Pattern and 1 Matcher by if test. But if you know how to use it, I'm not sure to get the question ? Note that creating Pattern could be costly so avoid to create it at each call (baeldung.com/java-regex-pre-compile). By the way, maybe this is just a simple example to illustrate but in your simple case using regexep seems overkill. — sbernard
– sbernard, Commented Jul 1, 2022 at 16:32
input.startsWith("#") is a lot faster than input.matches("#.*"). Regular expressions are not the solution to every problem. — VGR
– VGR, Commented Jul 1, 2022 at 17:12
It is a simple example: the real problem is of course more complicated :) — lennelei
– lennelei, Commented Jul 4, 2022 at 12:55
@sbernard: the question was exactly that. In fact, I started using regex in Perl. And in Perl, it's very simple to code (no need to have as many objects as if statements). I found it strange to need as many Pattern/Matcher pairs as if statements and wanted to get advice thank you :) ! And yes, the real example is far more complicated. — lennelei
– lennelei, Commented Jul 4, 2022 at 13:05

AlexR · Accepted Answer · 2022-07-01 16:15:31Z

1

Yes, you should.

Here is the example.

Pattern p = Pattern.compile("Phone: (\\d{9})");
String str = "Phone: 123456789";
Matcher m = p.matcher(str);
if (m.find()) {
    String g = m.group(1); // g should hold 123456789
}

answered Jul 1, 2022 at 16:15

AlexR

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