Java 9 Module creation with code samples

One of the new features added by Java 9 is the module system. This article is the last part in a  3 part article. In Part 1, I gave a high level introduction to modules and the advantages that they provide. In Part 2,  I covered the details of what exactly a module is, what it consists of and other module internals. In this part, I will be explaining how to create and use a module in Eclipse.

 

See also Module Introduction and Module Internals

Creating a Module

As covered in my earlier article, a module is a group of packages that helps to organize code better.  Let us first create a Java project that has a module.

Step 1 – Ensure that Java 9 is installed and configured in Eclipse.

Step 2 – Create a new Java project. Enter a project name. Ensure that JDK 9 is selected.

 

Step 3 – Click Next. The following screen is shown:

Creating a Java 9 Module in Eclipse

 

Step 4: Click “Finish”. A screen for entering module name is shown as below:

Creating a Java 9 Module in Eclipse

 

Step 5 – Enter the module name as “com.learnjava.calculatormodule”

Creating a Java 9 Module in Eclipse

Step 6 – Click “Create”. The Java project is created successfully with the project structure as shown below. The module-info.java file is created. As covered in my earlier article, the “module-info.java” file contains information about the packages required by the module, exported by the module, etc.

Creating a Java 9 Module in Eclipse

 

 

Step 7 – Create new package “com.learnjava.calculator” in the project:

Creating a Java 9 Module in Eclipse

 

Step 8 – Create a class called Calculator in the package:

Creating a Java 9 Module in Eclipse

 

Step 9: Add the following code in the Calculator class:

public class Calculator {    public int add(int a,int b) {    return a+b;  }}

 

Step 10 – Specify the package to be exported in the module-info file:

Creating a Java 9 Module in Eclipse
So now, we have created a Java project with a module “com.learnjava.calculatormodule”. This module exports the com.learnjava.calculator that has the Calculator.java class.

Creating a Module Client

A module client is a separate module that uses code from another module. So let us write some code that uses the Calculator class.

Step 1 – Follow steps 1-5 above and create a new project “CalculatorClient” with a module “com.learnjava.calculatorclient” as follows:

Creating a Java 9 Module Client

Step 2 – Create a new package “com.learnjava.client” and a class “CalculatorClient” within that package:

Creating a Java 9 Module Client

Step 3 – Specify the required package in the module-info file:

Creating a Java 9 Module Client

So this means that the com.learnjava.calculatorclient module requires the com.learnjava.calculatormodule.  If this requires attribute is not specified here, the com.learnjava.calculatorclient module will not be able to access the com.learnjava.calculatormodule.

The above step will cause a compilation error since the com.learnjava.calculatormodule is not present on the build path.  So we need to fix the project setup as follows:

Step 4a: Right click on the project –> properties:

Creating a Java 9 Module Client

Step 4b: Click on “Add”.

Creating a Java 9 Module Client

Step 4c: Select CalculatorModule. Click OK

Creating a Java 9 Module Client

Step 4d: This adds the calculator module to the path. Click on “Apply And Close”:

Creating a Java 9 Module Client

Now the compilation error will go away.

Step 5: Add the following code to the CalculatorClient class:

package com.learnjava.client;import com.learnjava.calculator.Calculator;public class CalculatorClient {    public static void main(String args[]) {    Calculator calculator = new Calculator();    int result = calculator.add(5, 10);    System.out.println("Result is:"+result);  }}

So this code invokes the Calculator.add method from the com.learnjava.calculatormodule

Step 6: Run the CalculatorClient class. This will print the following output:

17

Edit

Conclusion

So in this article, we saw how to create and use a Java 9 module in Eclipse. This article is the final article in the Java 9 series.

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