Illegal escaping on a Perl-style hex notation example on https://dev.java/learn/regex/intro/

[willy-b]

On the latest version of https://dev.java/learn/regex/intro/ (archived as is at https://megalodon.jp/2026-0814-0023-31/https://dev.java:443/learn/regex/intro/ , snippet may not show on the archiver but should be in the html )

• For the Perl-style hex notation example for matcher patterns:

String hexPattern = "\x{" + Integer.toHexString(codePoint) + "}";

The example appears to be invalid due to illegal escaping (I have reported other typos in this series (at #212 ) , but did NOT author or modify this content):

jshell> String hexPattern = "\x{" + Integer.toHexString(codePoint) + "}";
|  Error:
|  illegal escape character
|  String hexPattern = "\x{" + Integer.toHexString(codePoint) + "}";
|                        ^

I think it should be:

String hexPattern = "\\x{" + Integer.toHexString(codePoint) + "}";

so that one, using "\x{...}" instead of "\x{...}" can successfully match:

jshell> int codePoint = 0x6771; 
codePoint ==> 26481

jshell> String hexPattern = "\\x{" + Integer.toHexString(codePoint) + "}";
hexPattern ==> "\\x{6771}"

jshell> "\u6771"
$37 ==> "東"

jshell> "\u6771".matches(hexPattern)
$38 ==> true

Thanks!

[willy-b]

(In the above, the Github markdown formatter is hiding one of the \\ as \ but it should be displayed as "using \\x{...} instead of \x{...} can successfully match" in one place where it does not appear that way)