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

Examining the legacy JDK


Java has been around for over two decades now. For the most part of its lifetime, there have been a few things that haven't changed. Let's focus our attention on two aspects of the JDK the way they were in Java 8 or earlier:

  • The JRE structure: The file and directory structure that Java Runtime Environment (JRE) is installed as when it is set up on a computer
  • The state of API encapsulation: The differences between the public Java APIs and the internal platform classes

The JRE structure

When you install the Java 8 Runtime Environment on any machine and examine the installed directory, you'll see, among other files and folders, the following two important directories:

  • A bin directory with executable files, an important one of which is the Java executable that lets you run Java programs
  • The lib directory with some key .jar files including the all-important rt.jar

You may not have had to deal with the rt.jar directly when coding in Java, but you should know that it's the single...