Trail: Essential Classes
Lesson: Regular Expressions

字符类

如果浏览 Pattern 类规范，你将看到总结支持的正则表达式结构的表。在“字符类”部分中，你将找到以下内容：

构造	描述
`[abc]`	a，b 或 c(简单类)
`[^abc]`	除 a，b 或 c 之外的任何字符(否定)
`[a-zA-Z]`	a 到 z，或 A 到 Z，包括(范围)
`[a-d[m-p]]`	a 到 d，或 m 到 p：[a-dm-p](联合)
`[a-z&&[def]]`	d，e 或 f(交叉)
`[a-z&&[^bc]]`	a 到 z，b 和 c 除外：[ad-z](减法)
`[a-z&&[^m-p]]`	a 到 z，但不是 m 到 p：[a-lq-z](减法)

左侧列指定正则表达式构造，而右侧列描述每个构造将匹配的条件。

注意: 短语“character class”中的“class”一词不是指 .class 文件。在正则表达式的上下文中，character class (字符类) 是括在方括号内的一组字符。它指定将成功匹配给定输入字符串中的单个字符的字符。

简单类

字符类的最基本形式是简单地将一组字符并排放在方括号内。例如，表达式 [bcr]at 将匹配单词“bat”，“cat”或“rat”，因为它定义了一个字符类(接受“b”，“c”，或“r”)作为其第一个字符。

 
Enter your regex: [bcr]at
Enter input string to search: bat
I found the text "bat" starting at index 0 and ending at index 3.

Enter your regex: [bcr]at
Enter input string to search: cat
I found the text "cat" starting at index 0 and ending at index 3.

Enter your regex: [bcr]at
Enter input string to search: rat
I found the text "rat" starting at index 0 and ending at index 3.

Enter your regex: [bcr]at
Enter input string to search: hat
No match found.

在上面的示例中，只有当第一个字母与字符类定义的字符之一匹配时，整体匹配才会成功。

否定

要匹配除了列出字符之外的所有字符，请在字符类的开头插入“^”元字符。该技术称为 negation (否定)。

 
Enter your regex: [^bcr]at
Enter input string to search: bat
No match found.

Enter your regex: [^bcr]at
Enter input string to search: cat
No match found.

Enter your regex: [^bcr]at
Enter input string to search: rat
No match found.

Enter your regex: [^bcr]at
Enter input string to search: hat
I found the text "hat" starting at index 0 and ending at index 3.

仅当输入字符串的第一个字符不包含字符类定义的任何字符时，匹配才会成功。

范围

有时你需要定义一个包含一系列值的字符类，例如字母“a 到 h”或数字“1 到 5”。要指定范围，只需在要匹配的第一个和最后一个字符之间插入“-”元字符，例如 [1-5] 或 [a-h]。你还可以在类中将不同的范围放在彼此旁边，以进一步扩展匹配的可能性。例如，[a-zA-Z] 将匹配字母表中的任何字母：a 到 z(小写)或 A 到 Z(大写)。

以下是范围和否定的一些示例：

Enter your regex: [a-c]
Enter input string to search: a
I found the text "a" starting at index 0 and ending at index 1.

Enter your regex: [a-c]
Enter input string to search: b
I found the text "b" starting at index 0 and ending at index 1.

Enter your regex: [a-c]
Enter input string to search: c
I found the text "c" starting at index 0 and ending at index 1.

Enter your regex: [a-c]
Enter input string to search: d
No match found.

Enter your regex: foo[1-5]
Enter input string to search: foo1
I found the text "foo1" starting at index 0 and ending at index 4.

Enter your regex: foo[1-5]
Enter input string to search: foo5
I found the text "foo5" starting at index 0 and ending at index 4.

Enter your regex: foo[1-5]
Enter input string to search: foo6
No match found.

Enter your regex: foo[^1-5]
Enter input string to search: foo1
No match found.

Enter your regex: foo[^1-5]
Enter input string to search: foo6
I found the text "foo6" starting at index 0 and ending at index 4.

联合

你还可以使用 unions (联合) 创建由两个或多个单独的字符类组成的单个字符类。要创建联合，只需将一个类嵌套在另一个类中，例如 [0-4[6-8]]。此特定联合创建一个与数字 0,1,2,3,4,6,7 和 8 匹配的单个字符类。

Enter your regex: [0-4[6-8]]
Enter input string to search: 0
I found the text "0" starting at index 0 and ending at index 1.

Enter your regex: [0-4[6-8]]
Enter input string to search: 5
No match found.

Enter your regex: [0-4[6-8]]
Enter input string to search: 6
I found the text "6" starting at index 0 and ending at index 1.

Enter your regex: [0-4[6-8]]
Enter input string to search: 8
I found the text "8" starting at index 0 and ending at index 1.

Enter your regex: [0-4[6-8]]
Enter input string to search: 9
No match found.

交集

要创建仅匹配其所有嵌套类共有的字符的单个字符类，请使用 &&，如 [0-9&&[345]]。此特定交集创建单个字符类，仅匹配两个字符类共有的数字：3,4 和 5。

 
Enter your regex: [0-9&&[345]]
Enter input string to search: 3
I found the text "3" starting at index 0 and ending at index 1.

Enter your regex: [0-9&&[345]]
Enter input string to search: 4
I found the text "4" starting at index 0 and ending at index 1.

Enter your regex: [0-9&&[345]]
Enter input string to search: 5
I found the text "5" starting at index 0 and ending at index 1.

Enter your regex: [0-9&&[345]]
Enter input string to search: 2
No match found.

Enter your regex: [0-9&&[345]]
Enter input string to search: 6
No match found.

这是一个显示两个范围交集的示例：

 
Enter your regex: [2-8&&[4-6]]
Enter input string to search: 3
No match found.

Enter your regex: [2-8&&[4-6]]
Enter input string to search: 4
I found the text "4" starting at index 0 and ending at index 1.

Enter your regex: [2-8&&[4-6]]
Enter input string to search: 5
I found the text "5" starting at index 0 and ending at index 1.

Enter your regex: [2-8&&[4-6]]
Enter input string to search: 6
I found the text "6" starting at index 0 and ending at index 1.

Enter your regex: [2-8&&[4-6]]
Enter input string to search: 7
No match found.

减法

最后，你可以使用 subtraction (减法) 来否定一个或多个嵌套字符类，例如 [0-9&&[^345]]。此示例创建一个匹配 0 到 9，except (除了) 数字 3,4 和 5 之外的所有内容的单个字符类。

 
Enter your regex: [0-9&&[^345]]
Enter input string to search: 2
I found the text "2" starting at index 0 and ending at index 1.

Enter your regex: [0-9&&[^345]]
Enter input string to search: 3
No match found.

Enter your regex: [0-9&&[^345]]
Enter input string to search: 4
No match found.

Enter your regex: [0-9&&[^345]]
Enter input string to search: 5
No match found.

Enter your regex: [0-9&&[^345]]
Enter input string to search: 6
I found the text "6" starting at index 0 and ending at index 1.

Enter your regex: [0-9&&[^345]]
Enter input string to search: 9
I found the text "9" starting at index 0 and ending at index 1.

现在我们已经介绍了如何创建字符类，你可能希望在继续下一部分之前查看 Character Classes table。