Java case-insensitive regex matching doesn't work with letter Ñ

Question

Consider this program:

import java.util.regex.Pattern;
public class xx {

    /*
     *  Ñ
     *  LATIN CAPITAL LETTER N WITH TILDE
     *  Unicode: U+00D1, UTF-8: C3 91
     */
    public static final String BIG_N = "\u00d1";

    /*
     *  ñ
     *  LATIN SMALL LETTER N WITH TILDE
     *  Unicode: U+00F1, UTF-8: C3 B1
     */
    public static final String LITTLE_N = "\u00f1";

    public static void main(String[] args) throws Exception {
        System.out.println(BIG_N.equalsIgnoreCase(LITTLE_N));
        System.out.println(Pattern.compile(BIG_N, Pattern.CASE_INSENSITIVE).matcher(LITTLE_N).matches());
    }
}

Since Ñ is the upper-case version of ñ, you would expect it to print:

true
true

but what it actually prints (java 1.7.0_17-b02) is:

true
false

Why?

Answer 1

By default, case-insensitive matching assumes that only characters in the US-ASCII charset are being matched. Unicode-aware case-insensitive matching can be enabled by specifying the UNICODE_CASE flag in conjunction with this flag.

http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html#CASE_INSENSITIVE

And for completeness; you or (|) the flags together.

Pattern.compile(BIG_N, Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE)