The most common method for returning control to Fast VM is through the RTL Entry points . These consist of approximately 25 entry points that the compiled code invokes directly. Object creation routines. Checking routines for array store and cast operations. Exception handling routine for throwing or catching exceptions.
Compilation routines for compiling methods into native machine code.
JNI provides the Java programmer a JVM-independent mechanism for writing native methods. JNI routines perform functions such as reading and writing a field, invoking a method, etc. Rather than add expensive checks to generated code, Fast VM establishes exception handlers to catch certain conditions. For example, instead of prefixing every pointer dereference with a check for a NULL pointer, Fast VM emits code without checks and establishes a signal handler which throws a NullPointerException after the program dereferences address zero. Both the Classic and Fast VMs use most JDK native methods.