The Java SE 8 Edition of The Java® Virtual Machine Specification incorporates all the changes that have been made to the Java Virtual Machine since the Java SE 7 Edition in 2011. In addition, numerous corrections and clarifications have been made to align with popular implementations of the Java Virtual Machine.
This Edition continues the tradition of specifying the abstract Java Virtual Machine, serving as documentation for a concrete implementation only as a blueprint documents a house. An implementation of the Java Virtual Machine must embody this specification, but is constrained by it only where absolutely necessary.
Notable changes to the Java programming language in Java SE 8 have brought
corresponding changes to the Java Virtual Machine. To maximize binary compatibility,
it has been desirable to specify default methods directly in the
Java Virtual Machine, rather than relying on compiler magic that might not be
portable across vendors or product releases, and is certainly not
applicable to pre-existing
class files. In the context of JSR
335, Lambda Expressions for the Java Programming
Language, Dan Smith at Oracle consulted with implementers
to determine how best to integrate default methods into the constant
pool and method structures, the method and interface method resolution
algorithms, and the bytecode instruction set. JSR 335 also introduced
static methods in interfaces at the
level; they too have been carefully integrated with interface method
A theme of Java SE 8 is co-evolution of the Java SE platform libraries
with the Java Virtual Machine. A small but useful example is support for method
parameter names at run time: storing such names in the
structure goes hand in hand with offering a standard API to retrieve
illustrates an interesting development in the
class file structure
over the years: the First Edition of this specification defined six
attributes, of which three were deemed critical to the Java Virtual Machine, while
this Java SE 8 Edition defines 23 attributes, of which five are deemed
critical to the Java Virtual Machine; that is to say, attributes now exist primarily
to support libraries and tools rather than the Java Virtual Machine itself. To help
readers understand the
class file structure, this specification more
clearly documents the role of each attribute and the constraints
placed upon it.
Many colleagues in the Java Platform Group at Oracle have provided valuable support to this specification: Mandy Chung, Joe Darcy, Joel Borggrén-Franck, Staffan Friberg, Yuri Gaevsky, Jon Gibbons, Jeannette Hung, Eric McCorkle, Matherey Nunez, Mark Reinhold, John Rose, Georges Saab, Steve Sides, Bernard Traversat, Michel Trudeau, and Mikael Vidstedt. Particular thanks to Dan Heidinga (IBM), Karen Kinnear, Keith McGuigan, and Harold Seigel for their ironclad commitment to compatibility and security in popular Java Virtual Machine implementations.