Regular expressions simplify pattern-matching code - 1

Discover the elegance of regular expressions in text-processing scenarios that involve pattern matching

Text processing frequently requires code to match text against patterns. That capability makes possible text searches, email header validation, custom text creation from generic text (e.g., "Dear Mr. Smith" instead of "Dear Customer"), and so on. Java supports pattern matching via its character and assorted string classes. Because that low-level support commonly leads to complex pattern-matching code, Java also offers regular expressions to help you write simpler code.

Regular expressions often confuse newcomers. However, this article dispels much of that confusion. After introducing regular expression terminology, the java.util.regex package's classes, and a program that demonstrates regular expression constructs, I explore many of the regular expression constructs that the Pattern class supports. I also examine the methods comprising Pattern and other java.util.regex classes. A practical application of regular expressions concludes my discussion.

Note

Regular expressions' long history begins in the theoretical computer science fields of automata theory and formal language theory. That history continues to Unix and other operating systems, where regular expressions are often used in Unix and Unix-like utilities: examples include awk (a programming language that enables sophisticated text analysis and manipulation—named after its creators, Aho, Weinberger, and Kernighan), emacs (a developer's editor), and grep (a program that matches regular expressions in one or more text files and stands for global regular expression print).

What are regular expressions?

A regular expression, also known as a regex or regexp, is a string whose pattern (template) describes a set of strings. The pattern determines what strings belong to the set, and consists of literal characters and metacharacters, characters that have special meaning instead of a literal meaning. The process of searching text to identify matches—strings that match a regex's pattern—is pattern matching.