正則表達式量詞和字符類

Question

Java教程中提供了正則表達式量詞的示例和說明。

貪婪-先吃完整串然后再退一個字符然后重試

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

不情願-從頭開始，然后一次吃一個角色

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

擁有-嘗試一次嘗試吃整個字符串

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

它們還可以，我理解它們，但是有人可以向我解釋一下，將正則表達式更改為字符類時會發生什么？ 還有其他規定嗎？

 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

它將量詞（貪婪，不情願/懶惰，占有欲）應用於整個角色類。 這意味着它將匹配（貪婪地，懶惰地等）字符類中的每個文字字符。

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

因此它尋找f或x零個或多個。 引擎找到匹配的xf 。 它還匹配兩個o周圍的空字符串。 然后，它匹配連續的x ，因為它是f或x的零或更大 。

我會在regex101.com上查看有關regexes的更多詳細信息，尤其是左側欄中的調試器部分