The Java Tutorials have been written for JDK 8.Java教程是为JDK 8编写的。Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.本页中描述的示例和实践没有利用后续版本中引入的改进，并且可能使用不再可用的技术。See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.有关Java SE 9及其后续版本中更新的语言特性的摘要，请参阅Java语言更改。
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.有关所有JDK版本的新功能、增强功能以及已删除或不推荐的选项的信息，请参阅JDK发行说明。
If you browse through the 如果浏览Pattern class specification, you'll see tables summarizing the supported regular expression constructs. Pattern类规范，您将看到汇总支持的正则表达式构造的表。In the "Character Classes" section you'll find the following:在“字符类”部分，您将看到以下内容：
[abc] |
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[^abc] |
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[a-zA-Z] |
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[a-d[m-p]] |
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[a-z&&[def]] |
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[a-z&&[^bc]] |
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[a-z&&[^m-p]] |
The left-hand column specifies the regular expression constructs, while the right-hand column describes the conditions under which each construct will match.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。
.class file. .class文件。The most basic form of a character class is to simply place a set of characters side-by-side within square brackets. 字符类最基本的形式是将一组字符并排放在方括号内。For example, the regular expression 例如，的正则表达式[bcr]at will match the words "bat", "cat", or "rat" because it defines a character class (accepting either "b", "c", or "r") as its first character.[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.
In the above examples, the overall match succeeds only when the first letter matches one of the characters defined by the character class.在上面的示例中，仅当第一个字母与character类定义的字符之一匹配时，整体匹配才会成功。
To match all characters except those listed, insert the "要匹配除了列出的字符外的所有字符，请在字符类的开头插入“^" metacharacter at the beginning of the character class. ^”元字符。This technique is known as negation.这种技巧被称为否定。
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.
The match is successful only if the first character of the input string does not contain any of the characters defined by the character class.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。
Sometimes you'll want to define a character class that includes a range of values, such as the letters "a through h" or the numbers "1 through 5". 有时，您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”。To specify a range, simply insert the "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，如[1-5]或[a-h]。-" metacharacter between the first and last character to be matched, such as [1-5] or [a-h]. You can also place different ranges beside each other within the class to further expand the match possibilities. 您还可以在类中将不同的范围并排放置，以进一步扩展匹配的可能性。For example, 例如，[a-zA-Z] will match any letter of the alphabet: a to z (lowercase) or A to Z (uppercase).[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）。
Here are some examples of ranges and negation:下面是一些范围和否定的示例：
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.
You can also use unions to create a single character class comprised of two or more separate character classes. 还可以使用并集创建由两个或多个单独的字符类组成的单个字符类。To create a union, simply nest one class inside the other, such as 要创建并集，只需将一个类嵌套在另一个类中，例如[0-4[6-8]]. [0-4[6-8]]。This particular union creates a single character class that matches the numbers 0, 1, 2, 3, 4, 6, 7, and 8.这个特定的并集创建一个与数字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.
To create a single character class matching only the characters common to all of its nested classes, use 要创建仅匹配其所有嵌套类的公共字符的单个字符类，请使用&&, as in [0-9&&[345]]. &&，如[0-9&&[345]]。This particular intersection creates a single character class matching only the numbers common to both character classes: 3, 4, and 5.此特定交集创建一个仅与两个字符类（3、4和5）共有的数字匹配的单个字符类。
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.
And here's an example that shows the intersection of two ranges:下面是一个示例，显示了两个范围的交点：
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.
Finally, you can use subtraction to negate one or more nested character classes, such as 最后，可以使用[0-9&&[^345]]. 差集对一个或多个嵌套字符类求反，例如[0-9&&[^345]]。This example creates a single character class that matches everything from 0 to 9, except the numbers 3, 4, and 5.本例创建一个单字符类，该类匹配从0到9的所有内容，数字3、4和5除外。
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.
Now that we've covered how character classes are created, You may want to review the Character Classes table before continuing with the next section.既然我们已经介绍了角色类是如何创建的，那么在继续下一节之前，您可能需要查看字符类表。