JASM is an assembler/disassembler for JVM bytecode. It provides a nice syntax for writing JVM classes in a bytecode-focused assembly language, and can also disassemble any Java .class file to JASM ...
While the basic course is free and great for getting started, they also have a ‘Pro’ version if you want to dig deeper. It’s a solid choice if you’re totally new to programming and want a smooth, ...