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


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:




Match m zero or more times


Match m one or more times


Match m one or zero times (also called an optional match)


Match m exactly X times


Match mX or more times


Match m at least X and at most Y times


In all the aforementioned cases, m can be a single character or a group of characters. We will discuss grouping in more detail later.

Examples using quantifiers

Let's look at few examples to understand these basic quantifiers better.

Which regex pattern should be used to match a two-digit year or a four-digit...