Java9: Working with two or more modules

In my previous post, I explained how to create run ‘Hello World’ application using java9 modularity. In this post, I am going to explain how can you work with two or more modules together.

As you see above image, there are two modules.

a. main

b. math.arithmetic

'main.arithmetic' module contains all the packages and classes that are used to perform arithmetic operations. 'main' module depends on 'main.arithmetic' module to compute arithmetic operations.

Step 1: Create main.arithmetic module.

Create ArithmeticUtil.java and module-info.java files by following below directory structure.

$tree schoolmath/
schoolmath/
└── src
    └── math.arithmetic
        ├── com
        │   └── sample
        │       └── util
        │           └── ArithmeticUtil.java
        └── module-info.java

ArithmeticUtil.java

package com.sample.util;

public class ArithmeticUtil {

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

    public static int sub(int a, int b) {
        return a - b;
    }

    public static int mul(int a, int b) {
        return a * b;
    }

    public static int div(int a, int b) {
        return a / b;
    }

}

module-info.java

module math.arithmetic{
   exports com.sample.util;
}

Above statement tells 'com.sample.util' package can be exposed outside of the module.

Step 2: Define 'main' module by following below directory structure.

$tree schoolmath/
schoolmath/
└── src
    ├── main
    │   ├── com
    │   │   └── sample
    │   │       └── app
    │   │           └── App.java
    │   └── module-info.java
    └── math.arithmetic
        ├── com
        │   └── sample
        │       └── util
        │           └── ArithmeticUtil.java
        └── module-info.java

9 directories, 4 files

App.java

package com.sample.app;

import com.sample.util.ArithmeticUtil;

public class App {

    public static void main(String args[]) {

        System.out.println("Sum of 10 and 20 is : " + ArithmeticUtil.add(10, 20));
        System.out.println("Subtraction of 10 and 20 is : " + ArithmeticUtil.sub(10, 20));
        System.out.println("Multiplication of 10 and 20 is : " + ArithmeticUtil.mul(10, 20));
        System.out.println("Division of 10 and 20 is : " + ArithmeticUtil.div(10, 20));

    }
}

module-info.java

module main{
    requires math.arithmetic;
}

Above snippet tells that, main module depends on 'math.arithmetic' module.

Step 3: Compile and run App.java.

go inside schoolmath directory and execute below command to compile the classes.

javac --module-source-path src -d out src/main/com/sample/app/App.java

$javac --module-source-path src -d out src/main/com/sample/app/App.java
$
$tree
.
├── out
│   ├── main
│   │   ├── com
│   │   │   └── sample
│   │   │       └── app
│   │   │           └── App.class
│   │   └── module-info.class
│   └── math.arithmetic
│       ├── com
│       │   └── sample
│       │       └── util
│       │           └── ArithmeticUtil.class
│       └── module-info.class
└── src
    ├── main
    │   ├── com
    │   │   └── sample
    │   │       └── app
    │   │           └── App.java
    │   └── module-info.java
    └── math.arithmetic
        ├── com
        │   └── sample
        │       └── util
        │           └── ArithmeticUtil.java
        └── module-info.java

18 directories, 8 files

Execute below command to run the application.

java --module-path out -m main/com.sample.app.App

$java --module-path out -m main/com.sample.app.App
Sum of 10 and 20 is : 30
Subtraction of 10 and 20 is : -10
Multiplication of 10 and 20 is : 200
Division of 10 and 20 is : 0

You can get complete working application here.

https://github.com/harikrishna553/java9/tree/master/schoolmath/src

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