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

Non-capturing groups

There are cases while building regular expressions when we don't really want to capture any text but just want to group a subpattern to apply a boundary assertion or quantifier. This is the case for using non-capturing groups. We can mark a group as a non-capturing group by adding a question mark and a colon right after the opening parenthesis.

Note that we can also place one or more mode modifiers between the question mark and the colon. The scope of the modifier used in this manner is only effective for that group.

For example, we can use a non-capturing group in our regex to match an even number of digits:


Since we are not really interested in capturing any text from a matched string, it is a good choice to use a non-capturing group here.

An example of a non-capturing group with the ignore case modifier is as follows:


Due to the presence of the i modifier, this capturing group will match all the alternations by ignoring the...