Environment Modeling: In JPF, Java class files can be processed in two different ways:
A) As ordinary Java classes managed and executed by the host JVM (e.g., standard Java library classes, JPF implementation classes)
B) As “modeled” classes managed and processed (verified) by JPF
We have to clearly distinguish between these two modes. In particular, JPF’s “Model” layer has its own class and object model, which is completely different than and incompatible with the hidden class and object models of the underlying host JVM executing JPF.
Each standard JVM supports a Java Native Interface (JNI), that is used to delegate execution from the JVM-controlled bytecode down into the platform-dependent native layer (machine code). This is normally used to interface certain functionalities such as I/O or graphics to the platform OS and architecture. JPF provides an analogous mechanism to lower the “execution” level in JPF from JPF-controlled bytecode into JVM-controlled bytecode. This mechanism is called Model Java Interface (MJI). It supports the creation of dedicated classes to be executed by the underlying JVM rather than JPF. Such classes are not model checked by JPF.