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

Understanding services


Let's begin our journey of understanding services with a concept that you should be very familiar with as a Java developer--polymorphism. It starts with one interface and (possibly multiple) implementations of that interface. Although interfaces are not strictly necessary for services, they are still a good place to start. Let's say you define a service interface called MyServiceInterface that looks like this:

    package service.api; 
    public interface MyServiceInterface { 
      public void runService(); 
    } 

Now you can have multiple modules containing classes that implement this interface. Since all those modules need access to this interface, let's throw this interface into a module of its own, called service.api, and expose the package that the interface MyServiceInterface is in. Then each implementation module can require the service.api module and implement MyServiceInterface.

Consider there are three implementations of MyServiceInterface in three corresponding...