The current version (2.3) is an Ant-based Netbeans IDE project (Netbeans 12, JDK 11).
From Netbeans IDE:
menu Team/Git/Clone, enter repository address https://github.com/jjazzboss/JJazzLab-X.git
let Netbeans create a new project from the cloned files
select the created project then right-click Build
Note: JJazzLab-X only embeds a very basic music generation for debugging purpose. See www.jjazzlab.com for an example with a more powerful rhythm generation engine.