Oracle JRockit

Code generation strategies

There are several ways of executing bytecode in a JVM, from just emulating the bytecode in a pure bytecode interpreter to converting everything to native code for a particular platform.

Pure bytecode interpretation

Early JVMs contained only simple bytecode interpreters as a means of executing Java code. To simplify this a little, a bytecode interpreter is just a main function with a large switch construct on the possible opcodes. The function is called with a state representing the contents of the Java evaluation stack and the local variables. Interpreting a bytecode operation uses this state as input and output. All in all, the fundamentals of a working interpreter shouldn't amount to more than a couple of thousand lines ...