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

The union of character classes

The union of character classes will match a character that would be matched by any of the composing character classes. Essentially, this is the definition of the union operation in general. In regular expressions, it is possible to create unions of character classes by simply writing a character class inside another.

You may remember that character classes open with the [ character and close with the ] character, and we can list characters and character ranges between the opening and closing brackets.

In addition to those, we can use other character sets inside the brackets, and the resulting set will be the union of all these character classes. This way, there is no union operator to create the composition of these character classes; we just simply write them inside each other.

For example, consider the following composite character class:


This matches any character in the range of A to D or any single character P, Q, or R. This regular expression can...