blocks|key|3238029|text|正如maaartinus在他的评论中指出的那样，Java+(至少在理论上)为不区分大小写的reg-exp匹配提供了Unicode支持。Java+API文档中的措辞是匹配是“以与Unicode标准一致的方式”完成的。然而，问题是Unicode标准为大小写转换和不区分大小写的匹配定义了不同的支持级别，并且API文档没有指定Java语言支持的级别。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3238030|尽管没有文档记录，但至少在Oracle的Java+VM中，reg-exp实现仅限于所谓的简单的不区分大小写的匹配。与您的示例数据相关的限制因素是，只有当案例折叠(转换)产生相同数量的字符并且集合(例如".")时，匹配算法才能按预期工作。限制为只匹配输入字符串中的一个字符。第一个限制甚至会导致“«”与"SS“不匹配，这也是您可能已经预料到的。|3238031|要获得对字符串字面量之间完全不区分大小写的匹配的支持，可以在ICU4J+library中使用reg-exp实现，以便至少匹配“§”和"SS“。AFAIK，但是没有完全支持组、集合和通配符的Java的reg-exp实现。|offset|length|3238032|entityMap|0|LINK|mutability|MUTABLE|url|http://userguide.icu-project.org/strings/regexp^0|0|0|U|D|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

As maaartinus pointed out in his comment, Java provides (at least in theory) Unicode support for case-insensitive reg-exp matching. The wording in the Java API documentation is that matching is done "in a manner consistent with the Unicode Standard". The problem is however, that the Unicode standard defines different levels of support for case conversion and case-insensitive matching and the API documentation does not specify which level is supported by the Java language. 

Although not documented, at least in Oracle's Java VM, the reg-exp implementation is limited to so called simple case-insensitive matching. The limiting factors relevant to your example data is that the matching algorithm only works as expected if the case folding (conversion) results in the same number of characters and that sets (e.g. ".") are limited to match exactly one character in the input string. The first limitation even leads to "ß" not matching "SS", as you also may have had expected.

To get support for full case-insensitive matching between string literals, you can use the reg-exp implementation in the <a href="http://userguide.icu-project.org/strings/regexp" rel="nofollow">ICU4J library</a>, so that at least "ß" and "SS" matches. AFAIK, there are however no reg-exp implementations for Java with full support for groups, sets and wild cards.

It sounds like a joke, but I can sort of prove it.

Assumptions:

<ul>
<li>Dot matches any single character.</li>
<li>A case-insensitive pattern matches <code>s</code> if and only if it matches <code>s.toUpperCase()</code>.</li>
</ul>

All of the following is pretty logical and holds in Java:

<ul>
<li><code>"ﬃ".matches(".")</code> LATIN SMALL LIGATURE FFI (U+FB03) is a character, so it must match</li>
<li><code>"ß".matches(".")</code> LATIN SMALL LETTER SHARP S (U+00DF) is a character, so it must match</li>
<li><code>"ﬃ".toUpperCase().equals("FFI")</code> by the Unicode standard (there's no capital ligature FFI)</li>
<li><code>"ß".toUpperCase().equals("SS")</code> by the Unicode standard (there's a capital sharp S, but it doesn't get used)</li>
<li><code>"FfI".toUpperCase().equals("FFI")</code> obviously</li>
<li><code>"sS".toUpperCase.equals("SS")</code> obviously</li>
</ul>

So assuming the first dot in the regex stands for <code>ﬃ</code> and the second for <code>ß</code>, the regex must match "FFISS" and because of the case insensivity also "FfIsS".

I really do hope there's something wrong, otherwise regexes would get pretty unusable.

The questions:

<ul>
<li>What's wrong with my "proof"?</li>
<li>What does exactly "case insensitive" mean if my second assumption doesn't hold?</li>
</ul>

Assuming Unicode and case-insensitivity, should the pattern ".." match "FfIsS"?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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听起来像个笑话，但我可以证明这一点。假设：点匹配任何单个字符。不区分大小写的模式匹配s当且仅当它与Dot匹配下面的所有内容在Java中都是非常符合逻辑的：拉丁文小写连字"ﬃ".matches(".") ( match"ﬃ".toUpperCase().equals("FFI") )是一个字符，所以它必须由Unicode...

假设Unicode和不区分大小写，则模式"..“匹配"FfIsS"？-腾讯云开发者社区-腾讯云

问假设Unicode和不区分大小写，则模式"..“匹配"FfIsS"？
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