Programming for the Java™ Virtual Machine

Chapter 9. Inside a Java class File

Your first Java program probably looked something like this:

public class hello
{
   public static void main(String argv[])
   {
      System.out.println("Hello, world");
   }
}

You ran it through the Java compiler

> javac hello.java

to create the file hello.class. Then you ran the program

> java hello
Hello, world
>

and exulted in having mastered another programming language.

The hello.class file contains a Java virtual machine bytecode class that produces the intended effect of hello.java. The file hello.class is called a class file. The class file format is described in chapter 4 of The Java Virtual Machine Specification. All JVM implementations are required to treat this file in the same way. This is the heart of the “Write ...