Regular expressions simplify pattern-matching code - 8

Predefined character classes

Some character classes occur often enough in regexes to warrant shortcuts. Pattern provides such shortcuts with predefined character classes, which Table 1 presents. Use predefined character classes to simplify your regexes and minimize regex syntax errors.
Table 1. Predefined character classes

Predefined character class Description \d A digit. Equivalent to [0-9]. \D A nondigit. Equivalent to [^0-9]. \s A whitespace character. Equivalent to [ \t\n\x0B\f\r]. \S A nonwhitespace character. Equivalent to [^\s]. \w A word character. Equivalent to [a-zA-Z_0-9]. \W A nonword character. Equivalent to [^\w].

The following command-line example uses the \w predefined character class to identify all word characters in its text command-line argument:

java RegexDemo \w "aZ.8 _"

The command line above produces the following output, which shows that the period and space characters are not considered word characters:

Regex = \w

Text = aZ.8 _

Found a

  starting at index 0 and ending at index 1

Found Z

  starting at index 1 and ending at index 2

Found 8

  starting at index 3 and ending at index 4

Found _

  starting at index 5 and ending at index 6

Note

Pattern's SDK documentation refers to the period metacharacter as a predefined character class that matches any character except for a line terminator—a one- or two-character sequence identifying the end of a text line—unless dotall mode (discussed later) is in effect. Pattern recognizes the following line terminators: The carriage-return character (\r\) The new-line (line feed) character (\n) The carriage-return character immediately followed by the new-line character (\r\n) The next-line character (\u0085) The line-separator character (\u2028) The paragraph-separator character (\u2029)