Java 9 – Module System

Java 9, a new kind of programming component called module has been introduced. A module is a self-describing collection of code and data and has a name to identify it.

Features

With the Modules component, following enhancements has been added in Java 9 −

1. A new optional phase,link time, is introduced. This phase is in-between compile time and run time. During this phase, a set of modules can be assembled and optimized, making a custom runtime image using jlink tool.
2. javac, jlink, and java have additional options to specify module paths, which further locate definitions of modules.
3. JAR format updated as modular JAR, which contains module-info.class file in its root directory.
4. JMOD format introduced, a packaging format (similar to JAR) which can include native code and configuration files.

Creating Module

Following the steps to create a module say com.hi.techpoints.

Step 1

Create a folder C:\>JAVA\src. Now create a folder com.hi.techpoints which is same as the name of module we’re creating.

Step 2

Create module-info.java in C:\>JAVA\src\com.hi.techpoints folder with following code.

module-info.java

module com.hi.techpoints { }

module-info.java is the file which is used to create module. In this step we’ve created a module named com.tutorialspoint.greetings. By convention this file should reside in the folder whose name is same as module name.

Step 3

Add the source code in the module. Create Java9Module.java in C:\>JAVA\src\com.hi.techpoints\com\hi\techpoints folder with following code.

Java9Module.java

package com.hi.techpoints;

public class Java9Module {
   public static void main(String[] args) {
      System.out.println("Hello World!");
   }
}

By convention, the source code of a module to lie in same directory which is the name of the module.

Step 4

Create a folder C:\>JAVA\mods. Now create a folder com.hi.techpoints which is same as the name of module we’ve created. Now compile the module to mods directory.

C:/ > JAVA > javac -d mods/com.hi.techpoints 
   src/com.hi.techpoints/module-info.java 
   src/com.hi.techpoints/com/hi/techpoints/Java9Module.java

Step 5

Let’s run the module to see the result. Run the following command.

C:/>JAVA>java --module-path mods -m com.hi.techpoints/com.hi.techpoints.Java9Module 

Here module-path provides the module location as mods and -m signifies the main module.

Output

It will print the following output on console.

Hello World!