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Java 9 Regular Expressions
Java 9 Regular Expressions

Java 9 Regular Expressions: A hands-on guide to implement zero-length assertions, back-references, quantifiers, and many more

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Java 9 Regular Expressions

Understanding the Core Constructs of Java Regular Expressions

Using Java as a regular expression flavor, in this chapter, we will go a bit deeper and learn in detail about anchors, quantifiers, boundary matchers, all the available character classes, negated character classes, predefined character classes, and character classes escaping rules, using Java as a reference point. You will also learn Unicode text matching, using regular expressions in Java. We will also cover greedy versus non-greedy (lazy matching) and the change of regular expression behavior with lazy matching.

We will cover the following topics in this chapter:

  • Anchors and quantifiers
  • Boundary matchers
  • Character classes
  • Regex escaping rules
  • Escaping inside character classes
  • Negated character classes
  • Predefined character classes
  • Unicode characters matching
  • Greedy quantifiers
  • Lazy quantifiers
  • Possessive quantifiers...

Understanding the core constructs of regular expressions

Certain special character constructs are allowed literally in Java regular expressions. Here they are:

Special Character Meaning
\0c A character with the octal value c
\0cc A character with the octal value cc
\0ncc A character with the octal value ncc, where n cannot be more than 3
\xhh A character with the hexadecimal value 0xhh
\uhhhh A character with the hexadecimal value 0xhhhh
\x{h...h} A character with the hexadecimal value 0xh...h, where h must be a valid CODE_POINT
\n Newline character or u000A
\t Tab character or u0009
\r Carriage return character or u000D
\f Form feed character or u000C
\e Escape character or u\u001B
\a Bell character or \u0007
\cn A control character represented by n

Quantifiers

We briefly looked at quantifiers in the first chapter. Quantifiers allow us to quantify the occurrences of our matches. We can match the input in various ways, such as an optional match, an open-ended range, a closed range, and by using a fixed number. Let's take a closer look at them, as quantifiers are integral to most of the regular expressions.

Basic quantifiers

The following table lists all the quantifiers available in Java regular expressions:

...
Quantifier Meaning
m* Match m zero or more times
m+ Match m one or more times
m? Match m one or zero times (also called an optional match)
m{X} Match m exactly X times
m{X,} Match m X or more times
m{X,Y} Match m at least X and at most Y times

Summary

In this chapter, we covered the core constructs of regular expressions in depth. You learned anchors, quantifiers, boundary matchers, various character classes, negated character classes, and predefined character classes. We found out that escaped characters need to be escaped twice in the Java language. You also learned Unicode text matching using regular expressions in Java. We covered greedy, non-greedy, and possessive quantifiers. You learned embedded mode modifiers in Java regular expressions and how they can change the interpretation of a regular expression.

In the next chapter, we will cover another very important feature of regular expressions, called grouping. You will learn the various types of grouping available in Java regular expressions and how to use them.

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Key benefits

  • Discover regular expressions and how they work
  • Implement regular expressions with Java to your code base
  • Learn to use regular expressions in emails, URLs, paths, and IP addresses

Description

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.

Who is this book for?

This book is for Java developers who would like to understand and use regular expressions. A basic knowledge of Java is assumed.

What you will learn

  • Understand the semantics, rules, and core concepts of writing Java code involving regular expressions
  • Learn about the java.util.Regex package using the Pattern class, Matcher class, code snippets, and more
  • Match and capture text in regex and use back-references to the captured groups
  • Explore Regex using Java String methods and regex capabilities in the Java Scanner API
  • Use zero-width assertions and lookarounds in regex
  • Test and optimize a poorly performing regex and various other performance tips

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Jul 25, 2017
Length: 158 pages
Edition : 1st
Language : English
ISBN-13 : 9781787288034
Vendor :
Oracle
Category :
Languages :

What do you get with eBook?

Product feature icon Instant access to your Digital eBook purchase
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want

Product Details

Publication date : Jul 25, 2017
Length: 158 pages
Edition : 1st
Language : English
ISBN-13 : 9781787288034
Vendor :
Oracle
Category :
Languages :

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Table of Contents

8 Chapters
Getting Started with Regular Expressions Chevron down icon Chevron up icon
Understanding the Core Constructs of Java Regular Expressions Chevron down icon Chevron up icon
Working with Groups, Capturing, and References Chevron down icon Chevron up icon
Regular Expression Programming Using Java String and Scanner APIs Chevron down icon Chevron up icon
Introduction to Java Regular Expression APIs - Pattern and Matcher Classes Chevron down icon Chevron up icon
Exploring Zero-Width Assertions, Lookarounds, and Atomic Groups Chevron down icon Chevron up icon
Understanding the Union, Intersection, and Subtraction of Character Classes Chevron down icon Chevron up icon
Regular Expression Pitfalls, Optimization, and Performance Improvements Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Full star icon 5
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Amazon Customer Jun 08, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book is enough to have an in depth knowledge in Regular expressions.
Amazon Verified review Amazon
Justin Apr 19, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Amazingly insightful, here is a man that really knows his stuff and will help you figure out the most in depth problems. I would recommend this to anyone who actually wants to know how to solve problems with regex.
Amazon Verified review Amazon
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