如果浏览Pattern类规范会看到总结支持正则表达式结构的表。表13-1描述字符类。
左边一列指定正则表达式结构，右边一列描述每个结构在什么情况下匹配。
表13-1 字符类
|
[abc] |
a、b或者c（简单类） |
|
[^abc] |
除a、b或者c之外的任何字符（非） |
|
[a-zA-Z] |
a到z，或者A到Z（包含）（范围） |
|
[a-d[m-p]] |
a到d，或者m到p：[a-dm-p]（并） |
|
[a-z&&[def]] |
d、e或者f（交） |
|
[a-z&&[^bc]] |
a到z，除b和c之外：[ad-z]（减） |
|
[a-z&&[^m-p]] |
a到z，不包括m到p：[a-lq-z]（减） |
注意 短语“字符类”中“类”这个词不表示.class文件。在正则表达式的上下文表述中，字符类是括在方括号内的字符集合。它表示这些字符将和给定输入字符串内的单一字符成功匹配。
简单类
字符类最基本的形式是方括号中简单并排放置的字符集合。例如，正则表达式[bcr]at将和单词“bat”、“cat”或者“rat”匹配，因为它定义一个字符类（接受“b”、“c”或者“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.
在上面的例子中，只有当第一个字符和字符类定义的字符之一匹配时，整体匹配才成功。
1. 非
为了匹配列出的字符之外的所有字符，需要在字符类的开头插入“^”。这种技术被称为非（negation）：
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.
只有当输入字符串的第一个字符不包含字符类中定义的任何字符时，匹配才成功。
2. 范围
有时候，你会希望定义一个字符类包含一个范围内的值，比如字母“a”到“h”或者数字“1”到“5”。为了指定范围，只需在要匹配的第一个和最后一个字符之间插入“-”即可，比如[1-5]或者[a-h]。也可以在类中连着放置不同范围，以便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）或者A到Z（大写）。
下面是范围和非的一些例子：
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.
3. 并
也可以使用并（union）创建由两个或者多个独立字符类构成的单一字符类。为了创建并，只需在一个类中嵌套另一个类，比如[0-4[6-8]]。这个并创建的单一字符类匹配数字0、1、2、3、4、6、7和8。
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.
4. 交
为了创建只和其所有嵌套类共有的字符匹配的单一字符类，需要使用&&，比如[0-9&&[345]]。这个交创建只和两个字符类共有的数字（3、4和5）匹配的单一字符类：
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.
下面的例子显示两个范围的交：
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.
5. 减
最后，可以使用减（subtraction）去掉一个或者多个嵌套字符类，比如[0-9&&[^345]]。这个例子创建从0到9的所有值，但除3、4和5之外的单一字符类：
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.
现在我们介绍了如何创建字符类，在阅读下一小节之前你可能希望回顾一下表13-1。
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