↗️ This README only covers one section of the demo. The master branch contains more information.

The module monitor.stats has an optional dependency on stats.fancy. It's module descriptor uses requires static for that:

module monitor.statistics {
	requires monitor.observer;
	requires static stats.fancy;
	exports monitor.statistics;
}

To check whether the module is present, it uses the reflection API (see Statistician):

private boolean isModulePresent(String moduleName) {
	return this.getClass()
			.getModule()
			.getLayer()
			.findModule(moduleName)
			.isPresent();
}

Even though the module is on the module path, it is not resolved and thus not part of the module graphs unless:

• it is required (non-optionally) by some other module
• it is explicitly added to the graph during resolution

The first is not the case here. The second can be achieved by launching the app with --add-modules:

# add the optional dependency stats.fancy
java \
	--module-path mods \
	--class-path "libs/*" \
	--add-modules stats.fancy \
	--module monitor