You need Java 21 or newer to use Pi4J V3+. Please check the Prepare a Raspberry Pi and Install Java and Tools instructions. On a board with ARMv7 or ARMv8 you will get this result:
$ java -version
openjdk version "21.0.5" 2024-10-15 LTS
OpenJDK Runtime Environment Zulu21.38+21-CA (build 21.0.5+11-LTS)
OpenJDK 64-Bit Server VM Zulu21.38+21-CA (build 21.0.5+11-LTS, mixed mode, sharing)
Keep in mind this version is only compatible with ARMv7 or higher and doesn’t support all Raspberry Pi board versions. If you have a Raspberry Pi A (version 3), B (version 2 or higher), or Compute (version 3 or higher), you are good to go! For all other boards, or if you get the error below, you will need some additional steps that are described on Java for ARMv6/7/8.
$ java -version
Error occurred during initialization of VM
Server VM is only supported on ARMv7+ VFP
Pi4J is using Maven as build tool, this allows you to compile your code with the required modules into JAR-file thanks to the pom.xml configuration file which you can find in the root of a project. We need to install Maven and can do this with a single command, after which we can immediately check the installation by requesting the version:
$ sudo apt install maven
$ mvn -v
Apache Maven 3.6.0
Maven home: /usr/share/maven
Please check Prepare a Raspberry Pi > Install Visual Studio Code for more info if you want to develop Java code directly on the Raspberry Pi.