Writing a regex to detect repeat-characters [duplicate]

Question

I need to write a regex, that would identify a word that have a repeating character set at the end. According to the following code fragment, the repeating character set is An. I need to write a regex so this will be spotted and displayed.

According to the following code, \\w will match any word character (including digit, letter, or special character). But i only want to identify english characters.

String stringToMatch = "IranAnAn";
Pattern p = Pattern.compile("(\\w)\\1+");
Matcher m = p.matcher(stringToMatch);
if (m.find())
{
    System.out.println("Word contains duplicate characters " + m.group(1));
}

UPDATE

Word contains duplicate characters a
Word contains duplicate characters a
Word contains duplicate characters An

Answer 1

You want to catch as many characters in your set as possible, so instead of (\\w) you should use (\\w+) and you want the sequence to be at the end, so you need to add $ (and I have removed the + after \\1 which is not useful to detect repetition: only one repetition is needed):

Pattern p = Pattern.compile("(\\w+)\\1$");

Your program then outputs An as expected.

Finally, if you only want to capture ascii characters, you can use [a-zA-Z] instead of \\w:

Pattern p = Pattern.compile("([a-zA-Z]+)\\1$");

And if you want the character set to be at least 2 characters:

Pattern p = Pattern.compile("([a-zA-Z]{2,})\\1$");