正则表达式量词和字符类

Question

Java教程中提供了正则表达式量词的示例和说明。

贪婪-先吃完整串然后再退一个字符然后重试

 Regex: .*foo // greedy String to search: xfooxxxxxxfoo Found "xfooxxxxxxfoo" 

不情愿-从头开始，然后一次吃一个角色

 Regex: .*?foo // reluctant quantifier String to search: xfooxxxxxxfoo Found "xfoo", "xxxxxxfoo" 

拥有-尝试一次尝试吃整个字符串

 Regex: .*+foo // possessive quantifier String to search: xfooxxxxxxfoo No match found 

它们还可以，我理解它们，但是有人可以向我解释一下，将正则表达式更改为字符类时会发生什么？ 还有其他规定吗？

 Regex: [fx]* String to search: xfooxxxxxxfoo Found "xf","","","xxxxxxf","","","","" Regex: [fx]*? String to search: xfooxxxxxxfoo Found 15 zero-length matches Regex: [fx]*+ String to search: xfooxxxxxxfoo Found "xf","","","xxxxxxf","","","","" 

Answer 1

它将量词（贪婪，不情愿/懒惰，占有欲）应用于整个角色类。 这意味着它将匹配（贪婪地，懒惰地等）字符类中的每个文字字符。

Regex: [fx]*
String to search: xfooxxxxxxfoo
Found "xf","","","xxxxxxf","","","",""

因此它寻找f或x零个或多个。 引擎找到匹配的xf 。 它还匹配两个o周围的空字符串。 然后，它匹配连续的x ，因为它是f或x的零或更大 。

我会在regex101.com上查看有关regexes的更多详细信息，尤其是左侧栏中的调试器部分