Book Image

Modular Programming in Java 9

By : Koushik Srinivas Kothagal
Book Image

Modular Programming in Java 9

By: Koushik Srinivas Kothagal

Overview of this book

The Java 9 module system is an important addition to the language that affects the way we design, write, and organize code and libraries in Java. It provides a new way to achieve maintainable code by the encapsulation of Java types, as well as a way to write better libraries that have clear interfaces. Effectively using the module system requires an understanding of how modules work and what the best practices of creating modules are. This book will give you step-by-step instructions to create new modules as well as migrate code from earlier versions of Java to the Java 9 module system. You'll be working on a fully modular sample application and add features to it as you learn about Java modules. You'll learn how to create module definitions, setup inter-module dependencies, and use the built-in modules from the modular JDK. You will also learn about module resolution and how to use jlink to generate custom runtime images. We will end our journey by taking a look at the road ahead. You will learn some powerful best practices that will help you as you start building modular applications. You will also learn how to upgrade an existing Java 8 codebase to Java 9, handle issues with libraries, and how to test Java 9 applications.
Table of Contents (19 chapters)
Title Page
Credits
About the Author
About the Reviewers
www.PacktPub.com
Customer Feedback
Preface

Rethinking package structure


The fact that you are required to export package names from modules has an interesting implication on the way we organize our types into packages in Java 9. Historically, the package construct has been used by Java developers to provide namespaces for Java types. While these namespaces created by package names serve the purpose, at least in theory, to prevent type name collisions and to affect visibility of package-private member variables and types, they also serve a slightly more informal purpose of grouping related types for search-ability and maintainability of code.

There's an additional significance to packages in Java 9 that affects how you group your classes and other types into packages--visibility outside modules. For instance, if you need to hide type A within a module and export type B to outside the module, you are essentially required to place types A and B in two separate packages. In most cases, typical internal classes of libraries are associated...