The compiler turns Java source into bytecode. The JVM runs the bytecode. The JVM doesn’t need the compiler to run.
What I get from this is that the processor arch. Is dictated by the compiler at compile time, and by writing to bytecode directly we are skipping this.
I thought the proc. arch. was established by the manufacturer and was unavoidably implemented by the jni at runtime... unless there is an interface on top of the jn-interface to deal with the proc. But it seems absurd... why do this at compile time?
So somewhat confusingly, Java typically involves two compilers: one from source code to bytecode, the other from bytecode to native code. By nature, the first is processor-independent, the second is processor-dependent. The second happens at runtime on the target machine — thus, “write once, run anywhere”.