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.
Table of Contents (15 chapters)
Title page
About the Author
About the Reviewer
Customer Feedback
Free Chapter
Getting Started with Regular Expressions

Atomic groups

An atomic group is a non-capturing group that throws away all the alternative positions remembered by any token inside the group when the matching process exits the group after the first match of the pattern inside the group. Thus, it avoids backtracking to attempt all the alternatives present in the group.

Here is the syntax:


Here, the regex may contain alternative patterns. On the other hand, a non-atomic group will allow backtracking; it will try to find the first match and then if the matching ahead fails, it will backtrack and try to find the next match in alternation, until a match for the entire expression is found or all the possibilities are exhausted.

To understand it better, let's take an example of a regular expression using a non-atomic group:


The input string here is foodie.

It will match the starting pattern foo and then the first alternative d. It fails at this time because the end anchor, $, requires that we must be at the end of the...