Just reading about Java Bytecode manipulation in Ted Neward’s article on The Server Side, something I haven’t really made any investigations into before. Having done a little assembly in my past, it seems fairly straight forward. I guess the key points are:

• javap is a bytecode disassembler
• constants are defined in the constant-pool
• opcodes manipulate operands from the execution stack
• the execution stack is populated with operands
• categories of opcodes:
  • stack manipulation
  • branching and control flow
  • arithmetic
  • object model instructions (creating arrays of objects, setting fields, invoking methods, casting)
  • block synchronization
• exceptions are handled by an exception table that handles ranges of bytecode
• there are 212 current opcodes, with room for 46 more (all documented in JVM specification)
• Bill Venners book "Inside the Java Virtual Machine" would be a great place to start if I wanted to look into this further.