About the Raspberry Pi
The goal of the Raspberry Pi project was to build an inexpensive PC that is affordable for all. You can connect it to your TV if you don’t have a computer screen and different versions are available, depending on your budget (Fig. 1).
Figure 1: Raspberry A (3), B (4), and Zero
In 2019, the Raspberry Pi 4 was released with a 1.5 GHz 64-bit quad core ARM processor. Initially, with 1, 2, or 4GB, but with changing prices of memory, you can now buy the 2GB-version at the initial price of the 1GB-board, and an 8GB version was added. The prices range between 30 and 90€.
Last year in October the Raspberry Pi Compute 4 [1] (Fig. 2) got released. This is a board with the full Raspberry Pi 4 capabilities, but with connectors to plug it on a base-board you design yourself or buy, with the connections you need for your project. This makes it the ideal computer to integrate into your own device. There are 32 (yes 32!) different versions starting from 25€, depending on the amount of RAM and Flash, and optional wireless connectivity.
Figure 2: Raspberry Pi Compute 4
A month later the Raspberry Pi 400 [2] was added to the family. This is actually a Raspberry Pi 4 with 4GB built into a keyboard (Fig. 3). The processor is clocked at 1.8 GHz and thanks to a clever design, no fan is needed.
Figure 3: Raspberry Pi 400
If you want to have a quick start, buy a “Raspberry Pi 400” or the “Raspberry Pi 4 Desktop Kit” (around 130€) which includes the board, power supply, HDMI cables, case, and microSD card with the operating system pre-installed. You only need to add a mouse and monitor or TV.
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Why use a Raspberry Pi?
Yes indeed, for a little more money you can already find a laptop, but still, the price is very low! If you already have a power supply, cables, and/or microSD card, you can buy the board itself starting from 40€. Yep, indeed, that’s the starting price for a complete PC on a small board!
Another reason is the “Raspberry Pi OS (Full)” edition. There are different operating systems available for the Raspberry Pi, but the perfect starting point is provided by this version that can be copied to a microSD card with the free “Imager” tool [3] which you can find in the download section on the Raspberry Pi website.
When you use this OS you’re ready to start working from minute one, as these tools are pre-installed (Fig. 4):
Figure 4: Programming tools in Raspberry Pi OS
For Java development on the Raspberry Pi itself (Fig. 5), I prefer “Visual Studio Code” which is available in an ARM-version on their website [4], or just run “sudo apt install code -y”. If you want to experiment with a 64-bit OS (Ubuntu has one for the Raspberry Pi), you can also find an ARM64-bit version of VSC!
Figure 5: Visual Studio Code with Java Extension Pack and Maven on Raspberry Pi
The Raspberry Pi can also be your new best friend if you want to start experimenting with other programming languages. Make your choice: Java, Python, JavaScript, or start with the basics with Scratch. You can all run and use it on the Raspberry Pi. And as you can see in the above screenshot, multiple tools are available for all these programming languages.
But the main reason I fell in love with the Raspberry Pi is the GPIOs. When you look at the Raspberry Pi board, you’ll find 40 pins (2 rows of 20). Those are the GPIO (General-purpose input/output) pins. Some of those can be used as a digital input or output pin, meaning 0 Volt is off, 3.3 Volt is on. And the number of things you can do with it is amazing! These GPIOs pins are the main factors to make the Raspberry Pi such a success! You can indeed find a cheap second-hand laptop that includes a battery, screen, etc. but you’ll never be able to build experiments that combine soft- and hardware in such an easy way as you can do with the Raspberry Pi.
And one final pro for the Raspberry Pi: its power! The 4-version is fast and has a lot of memory. I wrote a full book on it and created a lot of different Java applications with it. You can connect up to two 4K monitors, which means a lot of space to have different applications, terminal, file explorer, etc. open at once. Already one such a 4K screen is a programmer’s heaven!
Pi4J, the Java I/O library for the Raspberry Pi
The Pi4J project aims to unite Java programming with electronics. The project started in 2012. Version 1.3 was released in February 2021 to support the newest Raspberry Pi boards (4, 400, and Compute 4) and is the last version which is based on Java 8. V1.4 is targeting Java 11 in the final test.
By using the Pi4J-dependency in a project, controlling electronic components connected to the GPIO (General Purpose Input/Output) pins of the Raspberry Pi can be controlled as objects in the Java code (Fig. 6). Pi4J uses native libraries to control the GPIOs so you as a programmer don’t need to fully be aware of all the “magic” which relates to hardware communication.
Fig. 6: The architecture of Pi4J – software to hardware
Work is ongoing for a totally refactored V2 which will bring modules and improved architecture to make the project easier to maintain, test and release. In the next articles in this series, we will use this V2 to show you how to program on the Raspberry Pi and control different electronic components.
Interview with Robert Savage
Robert is the founding father of the Pi4J project. He started in 2012 and quickly got a lot of attention from the Java community. Pi4J is now actively in use in a lot of projects. He also presented his work at the Devoxx 2014 and Oracle Code One 2019 conferences.
IoT Conference: The very first version of Pi4J dates from 2012. What was your trigger to start using Java on the Raspberry Pi and build this framework?
Robert Savage: Starting in the early ‘80s with my first Commodore VIC-20, I have enjoyed tinkering with computers and figuring out ways to get them to do useful tasks for me. When I first learned about the Raspberry Pi and its mission to provide a very affordable platform for education and hobbyists that struck a chord with me and sparked my interest to get involved in some way. Professionally, I had been involved for many years with embedded computers and microcontrollers but the Raspberry Pi represented something new (at that time)—a very powerful embedded computing device at a fraction of the cost of most embedded development platforms. I recognized this type of new device would be a game changer in the hobbyist community. Shortly after the first Java runtime was announced for the Raspberry Pi (back in the days of soft-float ABI), I immediately started looking for Java libraries to interact with the GPIO capabilities of the Pi. There were a couple of small projects out there but none that felt like Java programming. None offered an object-oriented approach to interact with the I/O. So in this void, I decided to create Pi4J and provide a more traditional API that Java users would be more comfortable and familiar with.
IoT Conference: Java was considered a long time to be a “big memory- and cpu-consuming beast”. So why do you think it is a good programming language to use on the Raspberry Pi?
Robert Savage: Java is a very capable and widely adopted language in the commercial world and has a long history in the embedded space. Continued improvements in the JVM on the ARM architecture make Java more relevant today than when Pi4J was first created. However, my original goals with Pi4J were not to eke out performance because it simply can’t compete with native programming for high performance or high-speed I/O requirements. Pi4J was created to simply enable Java programmers to enjoy access to the Raspberry Pi’s I/O capabilities and allow Java programmers to participate in the maker/hobbyist revolution of Linux-driven ARM-based SoCs brought on by the Raspberry Pi platform.
IoT Conference:: The Pi4J project is fully open-source and totally free. How do you manage to combine this with your professional and personal life?
Robert Savage: When I started the Pi4J project, there were a lot of synergies with my professional life and was at a time in my life prior to having children when I could burn the midnight oil without too many consequences/repercussions. In the past couple of years, committing the time needed to the project has become more difficult due to kids and trying to find a better work-life balance. I still very much enjoy working on the project and enjoy getting my hands dirty—but time is a bit more difficult to find. That is why I’m thankful that others have stepped in with a renewed interest in helping to move the project forward. We are trying to position the next version of Pi4J so that it’s a more community-led and driven effort and I’m not an obstacle or gatekeeper to forward progress.
IoT Conference: The Java world is now quickly evolving thanks to the 6-month release cycle and the new features that are being added. Do you see a match here with embedded programming?
Robert Savage: That is a tricky question. By nature, at least historically speaking, embedded systems tend to move very slowly to embrace changes. In the embedded world, stability and security are the primary goals. However, it can’t be denied that all modern development moves at a more rapid pace. I do think that as a library, Pi4J would still lag behind the bleeding edge just because you want to offer a solution that is widely compatible with the majority of user’s installed runtimes. As a library, you don’t want to be the forcing function that mandates a user’s application upgrade to the latest cutting-edge Java runtime version. So there is a balancing act that is required to embrace new runtime and language features but not cause upgrade pain points for your users. I think adopting the long term support (LTS) releases are best practice for library projects like Pi4J.
IoT Conference: What is the future for Pi4J and Java on the Raspberry Pi?
Robert Savage: My sincere hope is that Pi4J remains a viable and relevant resource for Java enthusiasts and continues to provide a simple object-oriented approach to interacting with the low-level IO offered on the RaspberryPi. I have always thought of Pi4J as the conduit allowing Java programmers to interact with the physical world and help abstract as much of the low-level complexity as possible. With greater community involvement and a new software architecture established in Pi4J version 2, I think we are much better positioned to embrace future changes and greater extensibility.
Building user interfaces with JavaFX
An important plus for Java on the Raspberry Pi is JavaFX. This framework allows you to build beautiful user interfaces which look and behave exactly the same on all devices, yes, also our Raspberry Pi! This means you only need to master one programming language for both the logic of your application, the user interface, and controlling electronic components when combined with Pi4J.
Although in the current trend a backend is mostly combined with a loosely coupled web-user interface, I strongly believe that one integrated solution is more performant and easier to build and maintain. That’s where Java and JavaFX are a perfect match.
Interview with Johan Vos
We asked Johan Vos, co-founder of Gluon, why Java on embedded devices is a hot topic. Gluon is the company leading the open-source development of JavaFX within the openjfx.io project. On their website [5], you can also find a lot of tools, documentation, and samples to get started with JavaFX.
IoT Conference: Java on embedded seems a controversial subject. Why do you believe Java, JavaFX, and the Raspberry Pi still are a perfect match?
Johan Vos: We have to distinguish between a few areas: branding and technical.
From a branding point, although Java started on embedded, it became popular in the enterprise and on backend/cloud systems. That sort of created the idea that Java was mainly suited for those big systems, and not for the resource-constrained devices. The server-side market is very different from the embedded, and that results in a different image/branding. However, the technology is the same.
From a technical point, Java was not very suited for small embedded devices for a long time, because of the overhead needed when a JDK had to be installed on every device. Fortunately, this is not valid anymore today. Thanks to AOT compilers (e.g. GraalVM native-image), it is possible to create native executables that contain everything that is needed to run a Java app on embedded devices.
Thanks to JavaFX, it is also possible to create a UI for embedded devices, using 100% the same Java APIs as desktop systems. In the past, the UI APIs for desktop (AWT/Swing) were different from the ones on embedded (e.g. PJava,…). With JavaFX, there is a clear separation between the top-level API’s and the low-level, platform-specific implementation. Especially on embedded, the JavaFX low-level implementations leverage the GPU and low-level stack to benefit from hardware acceleration.
In combination, this allows Java developers to create responsive applications for embedded, using the same tools they use for other Java applications.
IoT Conference: Java and JavaFX follow the same 6-months release cycle. Which improvements and new features are aiming at embedded platforms?
Johan Vos: The main goal is to keep the Java API the same for all platforms. Adding features that are specific to desktop, mobile, or embedded would break this idea. However, it should be possible to leverage specific (low-level) functionality for specific devices. We do this in a project called Gluon Attach [6] where a top-level Java API abstracts the low-level “details”.
IoT Conference: What can we expect in the near future for the Raspberry Pi in JavaFX?
Johan Vos: We’re working on more hardware acceleration for the Pi and embedded in general. This will lead to even more performance improvements and startup time.
The Gluon JavaFX 11 LTS program is also supporting embedded devices, which is an important guarantee that investments in Pi and embedded in general are secure for the next coming years.
IoT Conference: “Write once, run everywhere” has always been the goal of Java. Can we also include JavaFX and embedded in this story?
Yes, that is the idea from the previous questions: we don’t want specific APIs, we want Java APIs that have different implementations on different devices. Developers use those Java APIs and don’t have to worry about how they are implemented.
Conclusion
Yes, Java and JavaFX are a great match with the Raspberry Pi. Maybe you are not convinced yet, but in the next articles in this series, we will show you how to write Java code on the Raspberry Pi and make full use of its (GPIO) capabilities.
Links & Literature
[1] https://www.raspberrypi.org/products/compute-module-4-io-board/
[2] https://www.raspberrypi.org/products/raspberry-pi-400/
[3] https://www.raspberrypi.org/software/
[4] https://code.visualstudio.com/#alt-downloads
[5] https://gluonhq.com/developers/samples/
[6] https://github.com/gluonhq/attach
