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Joeq includes interpreters for both the Quad IR and the bytecode IR. These interpreters are implemented using the visitor design pattern. This makes it easy to modify the interpreter to gather profiling information -- simply make a new subclass of the interpreter that overrides the visit methods corresponding to the types of instructions that you care about.

Both interpreters have two modes of interpretation: direct and reflective. In direct interpretation, the interpreter uses the same stack as the compiled code, reading and writing values through direct memory accesses. Direct interpretation can only be used when Joeq is running natively. In reflective interpretation, the interpreter keeps a separate stack frame and performs all of the operations through reflection. Reflective interpretation can be used even when Joeq is running on a host virtual machine.

John Whaley 2003-03-15