Method and apparatus for automatically generating intermediate-level interfaces between program methods written in a platform-independent language and program methods written in a native language. A portable stub generator generates stubs in an intermediate, tokenized internal representation. The stub generator is portable across platforms as the stubs it generates are not platform-specific. In addition, the generated stubs are available to the compiler at intermediate compilation stages rather than at the backend compilation stage, and thus may be optimized together with the rest of the platform-independent code, and also may be inlined. The portable stub generator may be directed at virtual machine environments. An exemplary virtual machine environment in which the stub generator may be implemented is the Java™ Virtual Machine (JVM). In JVMs, Java™ is the platform-independent language, and Java™ bytecode the tokenized internal representation. In a JVM, the stubs may be generated in accordance with Java™ Native Interface (JNI).