Learn what JPMS improves in Java design, where it is worth the cost, and how module boundaries affect architecture.
JPMS, the Java Platform Module System, is about explicit boundaries. It gives Java a standard way to say which packages are exported, which dependencies are required, and which implementation details should stay hidden.
That matters most in large or long-lived systems where package conventions are not strong enough to prevent accidental coupling.
JPMS is not automatically a win for every codebase. The chapter sections that follow focus on the real architectural question: when does stronger module-level encapsulation justify the migration and tooling cost?