On Java 9+, the module system is always in play and there's nothing you can do about it. That is most obvious when you try to compile code that imports a class from an internal API (e.g. from a sun.* package) on such a version - it will fail due to strong encapsulation of (JDK) modules (unless you add JPMS-specific command line arguments).
But: You don't have to create modules at all. As long as you place your code and your dependencies on the class path, they all end up in the so-called unnamed module and there will be no encapsulation between them, the module system will not check presence of dependencies, split packages are ok, and so on and so forth. As the JDK team put it, "the chaos of the class path" lives on inside the unnamed module. But that doesn't mean the module system is not active - it is, just not within your code.
I'm so happy! And I wish to make this tiny ad happy too: