Question

I have the following code that can replace the email address in a String in Java:

addressStr.replaceFirst("([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})", "")

So, a string with John Smith <[e-mail]> would become John Smith <>. How do I negate it so that it will instead replace all that doesn’t match the email address and have the final result as just [e-mail]?

I tried to put in the ^ and ?<= at the front but it doesn’t work.

Answer 1

Well, it’s not the regex you need to change but the calling code. Your regex matches the e-mail address (in a weird way), and the replace() removes it from the string.

So just use

Pattern regex = Pattern.compile("([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})");
Matcher regexMatcher = regex.matcher(addressStr);
if (regexMatcher.find()) {
    address = regexMatcher.group();
}