Inside Java .class Files: How JVM Bytecode Structure Works

A technical deep-dive explains the internal binary structure of Java .class files generated by the javac compiler. Every valid .class file begins with the magic number CAFEBABE, followed by version bytes that identify the Java release — for example, major version 52 corresponds to Java 8. The article details how the JVM requires big-endian byte ordering for multi-byte numbers, which differs from the little-endian format used by most modern processors. A central component called the constant pool stores all program constants — including class names, method names, and type descriptors — referenced by the bytecode. The piece is part of a series building a Brainfuck-to-JVM bytecode compiler in Node.js, and uses xxd to inspect raw bytes of a minimal Hello.class file.