Java Cookbook, 1st Edition

Chapter 4. String Matching with Regular Expressions

4.0 Introduction

Suppose you have been on the internet for a few years and have been faithful about saving all your correspondence, just in case you (or your lawyers, or the prosecution) need a copy. The result is that you have a 5 GB disk partition dedicated to saved mail. Let’s further suppose that you remember that somewhere in there is an email message from someone named Angie or Anjie. Or was it Angy? But you don’t remember what you called it or where you stored it. Obviously, you have to look for it.

But while some of you might go and try to open up all 15 million documents in a word processor, I’ll just find it with one simple command. Any system that provides regular expression support allows me to search for the pattern in several ways. An easy one to understand is:

Angie|Anjie|Angy

which you can probably guess means just to search for any one of the variations. A more concise form (more thinking, less typing) is:

An[^ dn]

The syntax will become clear as we go through this chapter. Briefly, the “A” and the “n” match themselves, in effect finding words that begin with “An.” The cryptic [^ dn] requires the “An” to be followed by a character other than (^ means not in this context) a space (to eliminate the very common English word “an” at the start of a sentence), “d” (to eliminate the common word “and”) or “n” (to eliminate “Anne,” “Announcing,” etc.).

Has your word processor gotten past its splash screen yet? Well, ...