Chapter 8. Java

Java has had a native regex package, java.util.regex , since the early-2002 release of Java 1.4.0. It provides powerful and innovative functionality with an uncluttered (if somewhat simplistic) API. It has fairly good Unicode support, clear documentation, and fast execution. It matches against CharSequence objects, so it can be quite flexible in its application.

The original release of java.util.regex was impressive. Its feature set, speed, and relative lack of bugs were all of the highest caliber, especially considering that it was an initial release. The final 1.4 release was Java 1.4.2. As of this writing, Java 1.5.0 (also called Java 5.0) has been released, and Java 1.6.0 (also called Java 6.0 and "Mustang") is in its second beta release. Officially, this book covers Java 1.5.0, but I'll note important differences from Java 1.4.2 and the second 1.6 beta where appropriate. (The differences are also summarized at the end of this chapter ˜ 401.) ^{[ ]}

^{[ ]} This book covers Java 1.5.0 as of Update 7. The initial release of Java 1.5 had a severe bug related to case-insensitive matches. It was fixed in Update 2, so I recommend upgrading if youre running a prior version. The Java 1.6 beta information is current as of the second beta release, build 59g.

Reliance on Earlier Chapters Before looking at what's in this chapter, it's important to mention that it doesn't restate everything from Chapters 1 through 6. I understand that some readers interested only in Java may be inclined to start their reading with this chapter, and I want to encourage them not to miss the benefits of the preface and the earlier chapters: Chapters 1, 2, and 3 introduce basic concepts, features, and techniques involved with regular expressions, while Chapters 4, 5, and 6 offer important keys to regex understanding that apply directly to java.util.regex . Among the important concepts covered in earlier chapters are the base mechanics of how an NFA regex engine goes about attempting a match, greediness , backtracking, and efficiency concerns.

Table 8-1. Index of Methods

Sorted alphabetically , with page numbers
380 appendReplacement	373 matcher	379 replaceFirst
381 appendTail	376 matches (Matcher)	390 requireEnd
372 compile	395 matches (Pattern)	392 reset
377 end	393 pattern (Matcher)	395 split
375 find	394 pattern (Pattern)	377 start
394 flags	395 quote	394 text
377 group	379 quoteReplacement	377 toMatchResult
377 groupCount	386 region	393 toString (Matcher)
388 hasAnchoringBounds	386 regionEnd	394 toString (Pattern)
387 hasTransparentBounds	386 regionStart	388 useAnchoringBounds
390 hitEnd	378 replaceAll	393 usePattern
376 lookingAt	382 replaceAllRegion	387 useTransparentBounds
This table has been placed here for easy reference. The regex API discussion starts on page 371 .

Along those lines, let me emphasize that despite convenient tables such as the one in this chapter on page 367, or, for example, ones in Chapter 3 such as those on pages 114 and 123, this book's foremost intention is not to be a reference, but a detailed instruction on how to master regular expressions.

We've seen examples of java.util.regex in earlier chapters (˜ 81, 95, 98, 217, 235), and we'll see more in this chapter when we look at its classes and how to actually put it to use. First, though, we'll take a look at the regex flavor it supports, as well as the modifiers that influence that flavor.