CaseInsensitiveComparator java

最新推荐文章于 2024-07-10 09:18:29 发布

oYiMiYangGuang123

最新推荐文章于 2024-07-10 09:18:29 发布

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String 类看了忽略大小写的源码，觉得奇怪，源码如下，为什么大写不相等，还要判断小写呢，按说转成大写后不相等，转成小写就有可能相等吗

 private static class CaseInsensitiveComparator
            implements Comparator<String>, java.io.Serializable {
        // use serialVersionUID from JDK 1.2.2 for interoperability
        private static final long serialVersionUID = 8575799808933029326L;

        public int compare(String s1, String s2) {
            int n1 = s1.length();
            int n2 = s2.length();
            int min = Math.min(n1, n2);
            for (int i = 0; i < min; i++) {
                char c1 = s1.charAt(i);
                char c2 = s2.charAt(i);
                if (c1 != c2) {
                    c1 = Character.toUpperCase(c1);
                    c2 = Character.toUpperCase(c2);
                    if (c1 != c2) {
                        c1 = Character.toLowerCase(c1);
                        c2 = Character.toLowerCase(c2);
                        if (c1 != c2) {
                            // No overflow because of numeric promotion
                            return c1 - c2;
                        }
                    }
                }
            }
            return n1 - n2;
        }

        /** Replaces the de-serialized object. */
        private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
    }

public boolean regionMatches(boolean ignoreCase, int toffset,
        String other, int ooffset, int len)方法里有以下注释，原来是为了兼容the Georgian alphabet

if (ignoreCase) {
    // If characters don't match but case may be ignored,
    // try converting both characters to uppercase.
    // If the results match, then the comparison scan should
    // continue.
    char u1 = Character.toUpperCase(c1);
    char u2 = Character.toUpperCase(c2);
    if (u1 == u2) {
        continue;
    }
    // Unfortunately, conversion to uppercase does not work properly
    // for the Georgian alphabet, which has strange rules about case
    // conversion.  So we need to make one last check before
    // exiting.
    if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
        continue;
    }
}