Book Image

Java 9 Regular Expressions

By : Anubhava Srivastava
Book Image

Java 9 Regular Expressions

By: Anubhava Srivastava

Overview of this book

Regular expressions are a powerful tool in the programmer's toolbox and allow pattern matching. They are also used for manipulating text and data. This book will provide you with the know-how (and practical examples) to solve real-world problems using regex in Java. You will begin by discovering what regular expressions are and how they work with Java. This easy-to-follow guide is a great place from which to familiarize yourself with the core concepts of regular expressions and to master its implementation with the features of Java 9. You will learn how to match, extract, and transform text by matching specific words, characters, and patterns. You will learn when and where to apply the methods for finding patterns in digits, letters, Unicode characters, and string literals. Going forward, you will learn to use zero-length assertions and lookarounds, parsing the source code, and processing the log files. Finally, you will master tips, tricks, and best practices in regex with Java.

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Table of Contents (15 chapters)
Title page
Title page
Credits
Credits
About the Author
About the Author
About the Reviewer
About the Reviewer
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Preface
Preface
Free Chapter
1
Getting Started with Regular Expressions
Getting Started with Regular Expressions
Introduction to regular expressions
Summary
2
Understanding the Core Constructs of Java Regular Expressions
Understanding the Core Constructs of Java Regular Expressions
Understanding the core constructs of regular expressions
Quantifiers
Summary
3
Working with Groups, Capturing, and References
Working with Groups, Capturing, and References
Capturing groups
Non-capturing groups
Back references
Summary
4
Regular Expression Programming Using Java String and Scanner APIs
Regular Expression Programming Using Java String and Scanner APIs
Introduction to the Java String API for regular expressions' evaluation
Using regular expressions in Java Scanner API
Summary
5
Introduction to Java Regular Expression APIs - Pattern and Matcher Classes
Introduction to Java Regular Expression APIs - Pattern and Matcher Classes
The MatchResult interface
The Pattern class
The Matcher class
Summary
6
Exploring Zero-Width Assertions, Lookarounds, and Atomic Groups
Exploring Zero-Width Assertions, Lookarounds, and Atomic Groups
Zero-width assertions
\G boundary assertion
Atomic groups
Lookahead assertions
Lookbehind assertions
Summary
7
Understanding the Union, Intersection, and Subtraction of Character Classes
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
8
Regular Expression Pitfalls, Optimization, and Performance Improvements
Regular Expression Pitfalls, Optimization, and Performance Improvements
Common pitfalls and ways to avoid them while writing regular expressions
How to test and benchmark your regular expression performance
Catastrophic or exponential backtracking
Optimization and performance enhancement tips
Summary

Common pitfalls and ways to avoid them while writing regular expressions

Let's discuss some common mistakes people make while building regular expressions to solve various problems.

Do not forget to escape regex metacharacters outside a character class

You learned that all the special metacharacters, such as *, +, ?, ., |, (, ), [, {, ^, $, and so on, need to be escaped if the intent is to match them literally. I often see cases where programmers leave them unescaped, thus giving a totally different meaning to the regular expression. The Java regex API that we discussed in Chapter 5, Introduction to Java Regular Expressions APIs - Pattern and Matcher Classes, throws a non-checked exception if a regex pattern is wrongly formatted and cannot be compiled.

Avoid escaping every non-word character

Some programmers overdo escaping, thinking that they need to escape every non-word character such as colon, hyphen, semicolon, forward slash, and whitespace, which is not correct. They end up writing a regular...

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