Chapter 5. Modularity Patterns

Mastering a new technology or language feature in some ways feels like acquiring a new superpower. You immediately see the potential, and you want to change the world by applying it everywhere. If anything, superheroes from comics have shown us the world isn’t this black-and-white—even when you believe you have a superpower. Rarely is good and bad use of new powers immediately apparent; with great superpower comes great responsibility.

Learning the Java module system is no different. Knowing the module system does nothing for you if you do not also know about modular design principles to wield its power. Modularity is more than just an implementation concern, eased by the introduction of new language features. It’s a matter of design and architecture as well. Applying modular design also is a long-term investment. With it, you can hedge against changes in requirements, environments, teams, and other unforeseen events.

In this chapter, we discuss common patterns to improve the maintainability, flexibility, and reusability of systems built using modules. It’s essential to remember that many of these patterns and design practices are technology agnostic. Although there is code in this chapter, it serves to illustrate these sometimes abstract patterns in the context of the Java module system. The focus is on effectively modularizing a system by applying established patterns of modularity.

If these patterns seem obvious to you, congratulations! You’ve ...

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