How do the requires and exports directives in a module-info.java file work together to define a module's dependencies and public API surface?

requires ModuleName declares that your module depends on another named module, making that dependency's exported packages available to your module's own code (and causing a compile/runtime error if the required module isn't present, rather than a classpath-era silent NoClassDefFoundError potentially discovered much later); exports package.name declares that a specific package within YOUR module is accessible to OTHER modules that require yours, while any package NOT explicitly exported remains genuinely inaccessible outside your module (not just conventionally private, but JVM-enforced, rejecting even reflective access attempts by default) -- together these two directives let a module precisely control both what it needs and what it exposes.

// module-info.java for a library module
module com.example.mylibrary {
    requires java.logging;                    // this library itself depends on java.logging

    exports com.example.mylibrary.api;        // public API, visible to consuming modules
    // com.example.mylibrary.internal.impl is NOT exported -- truly hidden implementation detail
}

// A consuming module
module com.example.consumer {
    requires com.example.mylibrary;  // can now use com.example.mylibrary.api.* classes
    // but CANNOT access com.example.mylibrary.internal.impl.* at all -- compile error if attempted
}