concept automatic module in category java

This is an excerpt from Manning's book The Java Module System. Login to get full access to this book.

Automatic modules —Named modules without a module description (spoiler: plain JARs on the module path). These are application modules created by the runtime, not a developer.

Named modules —The set of explicit modules and automatic modules. These modules have a name, either defined by a descriptor or inferred by the JPMS.

But how do you decide where code needs to go? As a general guideline, the unnamed module is about compatibility, enabling projects using the class path to work on Java 9+; whereas automatic modules are about modularization, allowing projects to use the module system even if dependencies aren’t yet modularized.

Figure 8.6 With the plain JARs monitor.jar, monitor.observer.jar, and monitor.statistics.jar on the module path, the JPMS creates three automatic modules for them. The class-path content ends up in the unnamed module as before. Note how automatic modules read each other and the unnamed module, creating lots of cycles in the graph.

Automatic modules are full-fledged named modules, which means

> No module descriptor found. Derived automatic module.
>
> ${module-name}@${module-version} automatic
> requires java.base mandated