What is the difference between 'requires' and 'requires transitive', and how does transitive dependency propagation work in the module system?

A plain requires ModuleName gives your module access to that dependency's exported packages, but does NOT automatically propagate that access to modules that in turn require YOUR module (they'd need their own separate requires declaration for that same dependency if they need to use it directly); requires transitive ModuleName additionally propagates that dependency to any module requiring yours, meaning if module C requires module B (transitively), and module B requires transitive module A, then module C automatically also gains access to module A's exports without needing its own explicit requires A declaration -- this is specifically useful when your module's own public API directly exposes types from a dependency (like a method returning a type from that dependency), since consumers of your API genuinely need access to that dependency's types too, not just your own module's exports.

// module A (a shared library)
module com.example.geometry { exports com.example.geometry; }

// module B, whose PUBLIC API exposes types from module A
module com.example.shapes {
    requires transitive com.example.geometry;  // propagates geometry access to consumers of shapes
    exports com.example.shapes;  // shapes' public API includes methods returning geometry types
}

// module C, using shapes
module com.example.app {
    requires com.example.shapes;
    // Automatically ALSO has access to com.example.geometry's exports, via transitive propagation,
    // without needing 'requires com.example.geometry' explicitly here
}