Java不区分大小写的正则表达式匹配不适用于字母Ñ

Question

考虑这个程序:

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());
    }
}

由于Ñ是ñ的大写版本,你可以期望它打印:

true
true

但它实际打印的内容(java 1.7.0_17-b02)是:

true
false

为什么？

Answer 1

默认情况下,不区分大小写的匹配假定只匹配US-ASCII字符集中的字符.通过将UNICODE_CASE标志与此标志一起指定,可以启用Unicode感知的不区分大小写的匹配.

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

为了完整; 你或(|)标志在一起.

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