Strings and Regular Expressions - The Java Programming Language - page 474

13.3. Regular Expression Matching
The package java.util.regex provides you a way to find if a string
matches a general description of a category of strings called a regular
expression. A regular expression describes a class of strings by using
wildcards that match or exclude groups of characters, markers to require
matches in particular places, etc. The package uses a common kind of
regular expression, quite similar to those used in the popular perl pro-
gramming language, which itself evolved from those used in several Unix
utilities.
You can use regular expressions to ask if strings match a pattern and
pick out parts of strings using a rich expression language. First you will
learn what regular expressions are. Then you will learn how to compile
and use them.
13.3.1. Regular Expressions
A full description of regular expressions is complex and many other works
describe them. So we will not attempt a complete tutorial, but instead
will simply give some examples of the most commonly used features. (A
full reference alone would take several pages.) A list of resources for un-
derstanding regular expressions is in " Further Reading " on page 758 .
Regular expressions search in character sequences, as defined by
java.lang.CharSequence , implemented by String and StringBuilder . You can
implement it yourself if you want to provide new sources.
A regular expression defines a pattern that can be applied to a character
sequence to search for matches. The simplest form is something that is
matched exactly; the pattern xyz matches the string xyzzy but not the
string plugh . Wildcards make the pattern more general. For example, .
(dot) matches any single character, so the pattern .op matches both
hop and pop , and * matches zero or more of the thing before it, so xyz*
matches xy , xyz , and xyzzy .