Lets start with a few relevant reading material :
- First wikipedia article explaining what java bytecode is all about.
- The actual specification of Java bytecode, kindly engineered by Sun.
- The working developer's Guide to Java Bytecode, an article by TheServerSide.
- IBM article discussing Java byte and why you need it.
- Bytecode Basics the article at JavaWorld that was the trigger for my passion.
- A JVM Language Summit collection of presentations from InfoQ.
Continuing with some books that cover this topic from different angles. I hope that in due time I would be able to lay a better review about them... after I read them.
And here are some projects that deal with Java bytecode manipulation
These should give you a good starting point in exploring the Byte coded wonders of the JVM. Welcome to the world of "Real Programmers".
Last but not least, a link to some more tools and related artifacts for folks looking to toy with Bytecode http://www.artima.com/insidejvm/resources/index.html