As per my knowledge, there are 2 parts the answer you need.
1. Java Compiler(javac)
If you have studied compilers,
you should be familiar with the code generation mechanism. The code generated here, is Byte-Code, Bytecode are instructions which has, menomonic and opcode alike we have in x86 programming language. It is RISC instruction set.
For each construct like for, while, do-while, etc you have skeleton of code construct ready, it is just filled in and written to your .class file.
Now this .class file can be read by any VIRTUAL Machine which accepts bytecodes. In our case we use JVM.
2. JVM(java)
Now, here is the thing which runs your byte code. Alike we have processor to run machine instructions, we have JVM to run bytecode. But JVM is not a hardware entity, its a program in execution.
JVM has its register set, databus etc. implemented. These things are either implemented in CODE or it relies on capabilities of underlying hardware.
If you are interested in finding out more details you can see the following links:
http://en.wikipedia.org/wiki/List_of_Java_keywords
http://java.sun.com/docs/books/jvms/second_edition/html/Overview.doc.html#7143
Regards, Pushkaraj