Christian Stein

🎼 Bach.java - Intro 1 - Greetings!

Welcome to a series of blog posts describing how Bach.java builds a modular Java project.

This initial introduction prepares the foundation for more blog posts to come. The felt ratio of 99% IDEA-related sections to only 1% relevant for Bach.java is on purpose. Later posts will build upon this one and only refer to IDEA-related instructions covered here.

TL;DR

Create a modular Java project or clone/download bach-intro-1-greetings from GitHub

Run jshell https://sormuras.de/bach/build

Done

Fast-forward to the Build Modular Java Project with Bach.java section.

The remainder and the majority of the text sections below is about setting up IntelliJ IDEA for a modular Java project. In order to not re-invent wheels this blog borrows ideas and replays commands from the Module System Quick-Start Guide. It doesn’t hurt to (re-)visit that guide before reading on.

Without further a do, let’s start hacking … erm, clicking!

Prerequisite

Install IntelliJ IDEA

Screenshots for this blog post are taken from IDEA 2020.1.1 (Community Edition). An older version should be okay, too.

New Java Project

Click Create New Project on the Welcome Screen or via the Main Menu File/New/Project…
Select Java in the new project wizard
Select from Project SDK drop-down menu a Java version equal to 11 or higher

In this blog JDK 14.0.1 is used.

If you haven’t already installed a JDK 11+ on your machine, make use of IDEA’s excellent Download JDK… feature offered in the drop-down menu shown below.

Click Next to finish this step
Click Next to skip Create project from template page

Enter Basic Project Properties

Enter Greetings as the Project name
Choose a location for the project

The last path element should read Greetings
Append /.idea to the Module file location path in the More Settings group

Keeping all IDEA-related assets in one place, namely below the .idea/ directory.

Click Finish to close the new project wizard

A popup window may appear - click OK to let IDEA create the Greetings/.idea directory for you.

Fine-tune Project Settings

IDEA created an initial project structure. Some settings require a fine-tune pass.

IDEA has its own idea of storing all Java sources of an IDEA module in a nested src/ directory. In the following, we’ll delete and unmark such a src/ directory twice. Once per created IDEA module. Without the src/ directories the structure matches the example from the Quick-Start Guide better.

Open Project Structure dialog
Insert .idea element in the existing path of Project compiler output property as shown below

Why? To keep all IDEA-related assets in one place, here below the .idea/out directory.

Select src folder in Modules/Greetings/Sources
Press DEL key
Click Delete

Click Unmark Source as shown below

Click Apply to save the fine-tuning.

Add IDEA Module `com.greetings`

Let’s create an IDEA module named com.greetings. It will host the Java module with the same name.

Yes, as mentioned above, the hereby automatically created src/ directory will be deleted.

Click the + button at the top of the Project Settings/Modules page
Select New Module
Select Java – should be preselected, don’t add additional libraries and frameworks

Click Next
Enter com.greetings as Module name
Leave Content root as-is
Replace last element (com.greetings) with .idea in Module file location

Click Finish
Repeat deletion of the src folder as above and don’t forget to unmark it

Every IDEA module that hosts Java source files mandates at least a single Sources Folder to be selected. Here, the content root directory of the just created IDEA module is marked as such.

Select path ${BASE}/com.greetings (i.e. Content Root) from the Sources overview
Click/mark as Sources as shown below.

Click OK to close the Project Structure dialog

Add Java Module Descriptor `com.greetings`

With IDEA’s project structure set up and fine-tuned, let’s add Java source files. The Quick-Start Guide Greetings example reads:

The module consists of two source files: the module declaration (module-info.java) and the main class.

Right-click on the com.greetings IDEA module
Select New ▶ module-info.java

IDEA just generated an empty, yet proper Java Module Declaration for us!

Add Main Class `com.greetings.Main`

After declaring the Java module com.greetings, now it’s the turn of the main program.

Right-click on the com.greetings IDEA module, again
Select New ▶ Java Class

Enter the fully qualified class name: com.greetings.Main

IDEA just generated an empty Main.java file and stored in package com.greetings.

Add a main method that prints a greeting to the normal output stream

That’s it. All is set up for running the program.

Run Main Class with IDEA

Click on one of the Play icons next to the editor frame
Select ▶ Run ‘Main.main()’

Press Play On Tape …

Verify that the greeting message is printed and the process finished with exit code 0

Build Modular Java Project with Bach.java

Finally…

Open a Terminal session

Change to the base directory of the project, if necessary.
Type jshell https://sormuras.de/bach/build and press Enter

This URL redirects to the bach-build.jsh script. That JShell-based script forms the zero-installation feature of Bach.java.

Run jshell -R-Debug https://sormuras.de/bach/build to see what Bach.java is doing.

Wait some seconds to let the zero-installation feature bootstrap Bach.java and build the project.

Verify with .bach/workspace/image/bin/greetings that the main program is executable

of the Greetings project in the generated custom runtime image

Done.

Want more?

Here’s a short video showing Bach 11.8 in action: https://youtu.be/LyJ9BfZfEsI

Browse the .bach folder for generated assets: classes, modules, image, summaries, …
A summary of the last build is written to the .bach/summary.md file.
Attach some /** Javadoc */ comment to module com.greetings {} and run bach-build.jsh again.
Customize the build by editing the .bach/src/Build.java program.