Java 9 Regular Expressions · A Hands-On Guide to Implement Zero-Length Assertions, Back-References, Quantifiers, and Many More by Srivastava, Anubhava -- Read -- Imperial Library of Trantor

Index

Preface

What this book covers What you need for this book Who this book is for Conventions Reader feedback Customer support

Downloading the example code Errata Piracy Questions

Getting Started with Regular Expressions

Introduction to regular expressions

A bit of history of regular expressions Various flavors of regular expressions What type of problems need regular expressions to solve The basic rules of regular expressions Constructs of the standard regular expression and meta characters Some basic regular expression examples Eager matching

The effect of eager matching on regular expression alternation

Summary

Understanding the Core Constructs of Java Regular Expressions

Understanding the core constructs of regular expressions Quantifiers

Basic quantifiers

Examples using quantifiers

Greedy versus reluctant (lazy) matching using quantifiers Possessive quantifiers Boundary constructs

Examples using boundary constructs

Character classes

Examples of character classes Range inside a character class

Examples of character range

Escaping special regex metacharacters and escaping rules inside the character classes

Escaping inside a character class

Examples of escaping rules inside the character class

Literally matching a string that may contain special regex metacharacters Negated character classes

Examples of negated character classes

Predefined shorthand character classes

POSIX character classes

Unicode support in Java regular expressions

Commonly used Unicode character properties Negation of the preceding regex directives Unicode scripts support

Examples of matching Unicode text in regular expressions

Double escaping in a Java String when defining regular expressions Embedded regular expression mode modifiers The placement of embedded modes in a Java regular expression Disabling mode modifiers

Summary

Working with Groups, Capturing, and References

Capturing groups

Group numbering Named groups

Non-capturing groups

Advantages of non-capturing groups

Back references

Back reference of a named group Replacement reference of a named group Forward references Invalid (non-existing) backward or forward references

Summary

Regular Expression Programming Using Java String and Scanner APIs

Introduction to the Java String API for regular expressions' evaluation

Method - boolean matches(String regex)

Example of the matches method

Method - String replaceAll(String regex, String replacement)

Examples of the replaceAll method

Method - String replaceFirst(String regex, String replacement)

Examples of the replaceFirst method

Methods - String split methods

The limit parameter rules Examples of the split method

Example of the split method using the limit parameter

Using regular expressions in Java Scanner API Summary

Introduction to Java Regular Expression APIs - Pattern and Matcher Classes

The MatchResult interface The Pattern class

Examples using the Pattern class

Filtering a list of tokens using the asPredicate() method

The Matcher class

Examples using the Matcher class

Method Boolean lookingAt() The matches() method The find() and find(int start) methods

The appendReplacement(StringBuffer sb, String replacement) method The appendTail(StringBuffer sb) method Example of the appendReplacement and appendTail methods

Summary

Exploring Zero-Width Assertions, Lookarounds, and Atomic Groups

Zero-width assertions

Predefined zero-width assertions Regex defined zero-width assertions

\G boundary assertion Atomic groups Lookahead assertions

Positive lookahead Negative lookahead

Lookbehind assertions

Positive lookbehind Negative lookbehind Capturing text from overlapping matches Be careful with capturing groups inside a lookahead or lookbehind atomic group

Lookbehind limitations in Java regular expressions

Summary

Understanding the Union, Intersection, and Subtraction of Character Classes

The union of character classes The intersection of character classes The subtraction of character classes Why should you use composite character classes? Summary

Regular Expression Pitfalls, Optimization, and Performance Improvements

Common pitfalls and ways to avoid them while writing regular expressions

Do not forget to escape regex metacharacters outside a character class Avoid escaping every non-word character Avoid unnecessary capturing groups to reduce memory consumption However, don't forget to use the required group around alternation Use predefined character classes instead of longer versions Use the limiting quantifier instead of repeating a character or pattern multiple times Do not use an unescaped hyphen in the middle of a character class The mistake of calling matcher.goup() without a prior call to matcher.find(), matcher.matches(), or matcher.lookingAt() Do not use regular expressions to parse XML / HTML data

How to test and benchmark your regular expression performance Catastrophic or exponential backtracking

How to avoid catastrophic backtracking

Optimization and performance enhancement tips

Use a compiled form of regular expressions Use a negated character class instead of the greedy and slow .* or .+ Avoid unnecessary grouping Use lazy quantifiers strategically instead of greedy quantifiers that cause excessive backtracking Make use of possessive quantifiers to avoid backtracking Extract common repeating substrings out of alternation Use atomic group to avoid backtracking and fail fast

Summary

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