regex - Uppercase letters followed by any utf-8 lowercase characters

Question

I want to write a regex which is valid if it starts with IJ followed by any lowercase letters in utf-8.

private static String pattern = "^\\u0049\\u004A(\\p{Ll})*";
System.out.println(Pattern.compile(pattern).matcher("IJP").find()); // true

I am using this regex but it doesn't seem to work. For "IJP" it should not match as P is uppercase.

All you missed is `$`. Use anchors to make sure you match the entire string regardless of the regex method you are using (`find()` or `matches()`). — Wiktor Stribiżew, Sep 03 '20 at 20:14

score 1 · Accepted Answer · answered Sep 03 '20 at 18:59

Your pattern should be:

final String pattern = "^\\u0049\\u004A\\p{Ll}*$";

Note placement of $ in the end to make it 0 or more lowercase characters before end. Note that I have removed unnecessary group around \p{Ll}.

Code Demo:

jshell> String pattern = "^\\u0049\\u004A\\p{Ll}*$";
pattern ==> "^\\u0049\\u004A\\p{Ll}*$"

jshell> Pattern.compile(pattern).matcher("IJP").find();
$6 ==> false

score 0 · Answer 2 · answered Sep 03 '20 at 18:59

\\u0049 is a rather obtuse way of writing I, don't you think? Why not just... write pattern = "^IJ\\p{Ll}"?

IJP does match though. Think about it. You're asking for an I, then a J, then 0 or more lowercase letters. Which is right there: An I, a J, and 0 lowercase letters.

Either use matches() instead of find() (which asks: Does the ENTIRE string match the regexp, vs. 'is there some substring that does') or, as you've already thrown the ^ in there, toss a $ at the end to match.

To allow only if it's IJ, I used "^IJ\\p{Ll}*$" – user1298426 Sep 03 '20 at 19:21 — user1298426, Sep 03 '20 at 19:21

regex - Uppercase letters followed by any utf-8 lowercase characters

2 Answers2