2.13. Public Design, Private Implementation
Thus far this specification has sketched the public view of the Java Virtual Machine: the
class file format and the instruction set. These components are vital to the hardware-, operating system-, and implementation-independence of the Java Virtual Machine. The implementor may prefer to think of them as a means to securely communicate fragments of programs between hosts each implementing the Java SE platform, rather than as a blueprint to be followed exactly.
It is important to understand where the line between the public design and the private implementation lies. A Java Virtual Machine implementation must be able to read
class files and must exactly implement the semantics of the Java Virtual Machine ...