Refers to the module as defined by the Java Platform Module System in Java 9+.
A module in the Java Platform Module System is a named, self-describing collection of code and data. Its code is organized as a set of packages containing types, i.e., Java classes and interfaces; its data includes resources and other kinds of static information. The only module known specifically to the module system, in any case, is the base module, which is named java.base.
A module is described using a module-info, which itself is a new construct added in java-9 to provide a module definition.
Module names, like package names, must not conflict. The recommended way to name a module is to use the reverse-domain-name pattern that has long been recommended for naming packages. The name of a module will, therefore, often be a prefix of the names of its exported packages, but this relationship is not mandatory.
Module declarations are part of the Java programming language, rather than a language or notation of their own, for several reasons. One of the most important is that module information must be available at both compile time and run time in order to achieve fidelity across phases, i.e., to ensure that the module system works in the same way at both compile time and run time. This, in turn, allows many kinds of errors to be prevented or, at least, reported earlier—at compile time—when they are easier to diagnose and repair.
The Java SE 9 Platform Specification uses the module system to divide the platform into a set of modules. An implementation of the Java SE 9 Platform might contain all of the platform modules or, possibly, just some of them.
A java.lang.Module represents a run-time module, either named or unnamed.
Named modules have a name and are constructed by the Java Virtual Machine when a graph of modules is defined to the Java virtual machine to create a module layer.
An unnamed module does not have a name. There is an unnamed module for each ClassLoader, obtained by invoking its getUnnamedModule method. All types that are not in a named module are members of their defining class loader's unnamed module.
The package names that are parameters or returned by methods defined in this class are the fully-qualified names of the packages as defined in section 6.5.3 of The Java™ Language Specification, for example, java.lang.
