Learning about Java bytecode and the JVM

Question

In a recent question asked recently my simple minded answer highlighted many of my misconceptions about Java, the JVM, and how the code gets compiled and run. This has created

Answer 1

The Apache BCEL will allow you to analyse and hand craft .class files from bytecode.

javap will allow you to disassemble existing .class files. It's particularly useful for knocking up quick test classes to understand what is really going on underneath the covers.