Inserting hyphen between groups with Java regex issue

Question

I'm performing a test to find and replace a string of 3 or 4 capital letters followed by a number with that same string, a hyphen, and that same number. In Perl, I can use:

s/([A-Z]{3,4})([0-9])/$1-$2/g;

I've tried this in Java, hardcoding a string like:

public class Test {
    public static void main(String[] args) {
        String test = "TEST1";

        Pattern p = Pattern.compile("([A-Z]{3,4})([0-9])");

        Matcher m = p.matcher(test);
        if (m.find()) {
            m.replaceAll(m.group(1) + "-" + m.group(2));
        }
        System.out.println(test);

    }
}

But no match was found. Is my Java syntax wrong or is it a regular expression issue?

Answer 1

No need to use Pattern/Matcher, you can just do:

test = test.replaceAll( "([A-Z]{3,4})([0-9])", "$1-$2");

Answer 2

You just need to use a replaceAll with the regex you already have:

String test = "TEST1";
System.out.println(test.replaceAll("([A-Z]{3,4})([0-9])", "$1-$2"));

See IDEONE demo

This is from docs:

public String replaceAll(String regex, String replacement)
Replaces each substring of this string that matches the given regular expression with the given replacement.