Declaration

To declare a module, you need to create a file named module-info.java and put it at the top of the folder where your code is.

src/
  example/
    Example.java
  some/
    packageName/
      AClass.java
  module-info.java

Within this file you put module followed by a name for the grouping of packages and {}.¹

module example {
}

Just like with package names, module names can have multiple parts separated by .s.

module a.longer.name {
}

Nothing in this declaration says explicitly what packages are part of the module; it is just assumed that it holds the packages it is "next to."