The Java Virtual Machine Specification / Edition 2 available in Paperback
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The nucleus of the Java(TM) 2 platform, the Java(TM) virtual machine is the technology that enables the Java 2 platform to host applications on any computer or operating system without rewriting or recompiling. The Java virtual machine is also responsible for the compactness of applications targeting the Java 2 platform, and is the basis for its security capabilities.
This book was written by those directly responsible for the design and implementation of the Java virtual machine, and is the complete and definitive specification for the technology. It is an essential reference for writers of compilers for the Java programming language and implementors of the Java virtual machine. This second edition specifies the newest version of the Java virtual machine and provides a fascinating view into the inner workings of the Java 2 platform.
In this book you will find comprehensive coverage of the class file format, the hardware, operating system, and implementation-independent binary format for compiled code. The authors fully describe the instruction set of the Java virtual machine. You will find an entire chapter of examples that demonstrate how to compile code written in the Java programming language into the instruction set of the Java virtual machine. In addition, the book presents a discussion on the vital topic of Java virtual machine threads and their interaction with memory.
All in all, this comprehensive, detailed, and methodical presentation provides the information necessary to implement your own fully compatible Java virtual machine.
About the Author
Tim Lindholm, Distinguished Engineer in Java Software at Sun Microsystems, Inc., was an original member of the Java project at Sun. He was a key contributor to the Java programming language and remains the senior architect of the Java virtual machine and the Java 2 runtime environment. He is also the Technical Editor of The Java(TM) Series.
Frank Yellin, Staff Engineer in Embedded and Consumer at Sun Microsystems, Inc., was an original member of the Java project at Sun. He has spent a decade working on the runtime systems for interpreted and compiled languages. Previously he worked at Lucid, where he focused on multitasking, garbage collection, interrupts, and the compilation of Common Lisp.
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About the Java Series
The Java Series books provide definitive reference documentation for
Java programmers and end users. They are written by members of the
Java team and published under the auspices of JavaSoft, a Sun
Microsystems business. The World Wide Web allows Java
documentation to be made available over the Internet, either by
downloading or as hypertext. Nevertheless, the worldwide interest in
Java technology led us to write and publish these books to supplement all
of the documentation at our Web site.
We would like to thank the Corporate and Professional Publishing Group
at Addison-Wesley for their partnership in putting together the Series.
Our editor Mike Hendrickson and his team have done a superb job of
navigating us through the world of publishing. Within Sun, the support of
James Gosling, Ruth Hennigar, Jon Kannegaard, and Bill Joy ensured
that this series would have the resources it needed to be successful. In
addition to the tremendous effort by individual authors, many members of
the JavaSoft team have contributed behind the scenes to bring the highest
level of quality and engineering to the books in the Series. A personal
note of thanks to my children Christopher and James for putting a
positive spin on the many trips to my office during the development of the
Table of Contents
A Bit of History.
The Java Virtual Machine.
Summary of Chapters.
2. Java Programming Language Concepts.
Types and Values.
Primitive Types and Values.
Operators on Integral Values.
Floating-Point Types, Value Sets, and Values.
Operators on Floating-Point Values.
Operators on boolean Values.
Reference Types, Objects, and Reference Values.
The Class Object.
The Class String.
Operators on Objects.
Initial Values of Variables.
Variables Have Types, Objects Have Classes.
Conversions and Promotions.
Widening Primitive Conversions.
Narrowing Primitive Conversions.
Widening Reference Conversions.
Narrowing Reference Conversions.
Value Set Conversion.
Method Invocation Conversion.
Names and Packages.
The Members of a Class Type.
The Members of an Interface Type.
The Members of an Array Type.
Qualified Names and Access Control.
Fully Qualified Names.
Superclasses and Subclasses.
The Class Members.
Initialization of Fields.
Interface (Constant) Fields.
Interface (Abstract) Methods.
Overriding, Inheritance, and Overloading in Interfaces.
Nested Classes and Interfaces.
The Causes of Exceptions.
Handling an Exception.
The Exception Hierarchy.
The Classes Exception and RuntimeException.
Virtual Machine Start-up.
Linking: Verification, Preparation, and Resolution.
Detailed Initialization Procedure.
Creation of New Class Instances.
Finalization of Class Instances.
Unloading of Classes and Interfaces.
Virtual Machine Exit.
3. The Structure of the Java Virtual Machine.
The class File Format.
Primitive Types and Values.
Integral Types and Values.
Floating-Point Types, Value Sets, and Values.
The returnAddress Type and Values.
The boolean Type.
Reference Types and Values.
Runtime Data Areas.
The pc Register.
Java Virtual Machine Stacks.
Runtime Constant Pool.
Native Method Stacks.
Normal Method Invocation Completion.
Abrupt Method Invocation Completion.
Representation of Objects.
Java Virtual Machine Floating-Point Arithmetic and IEEE 754.
Value Set Conversion.
Specially Named Initialization Methods.
Instruction Set Summary.
Types and the Java Virtual Machine.
Load and Store Instructions.
Type Conversion Instructions.
Object Creation and Manipulation.
Operand Stack Management Instructions.
Control Transfer Instructions.
Method Invocation and Return Instructions.
Public Design, Private Implementation.
4. The class File Format.
The ClassFile Structure.
The Internal Form of Fully Qualified Class and Interface Names.
The Constant Pool.
The CONSTANT_Class_info Structure.
The CONSTANT_Fieldref_info, CONSTANT_Methodref_info, and CONSTANT_InterfaceMethodref_info Structures.
The CONSTANT_String_info Structure.
The CONSTANT_Integer_info and CONSTANT_Float_info Structures.
The CONSTANT_Long_info and CONSTANT_Double_info Structures.
The CONSTANT_NameAndType_info Structure.
The CONSTANT_Utf8_info Structure.
Defining and Naming New Attributes.
The ConstantValue Attribute.
The Code Attribute.
The Exceptions Attribute.
The InnerClasses Attribute.
The Synthetic Attribute.
The SourceFile Attribute.
The LineNumberTable Attribute.
The LocalVariableTable Attribute.
The Deprecated Attribute.
Constraints on Java Virtual Machine Code.
Verification of class Files.
The Verification Process.
The Bytecode Verifier.
Values of Types long and double.
Instance Initialization Methods and Newly Created Objects.
Exceptions and finally.
Limitations of the Java Virtual Machine.
5. Loading, Linking, and Initializing.
The Runtime Constant Pool.
Virtual Machine Start-up.
Creation and Loading.
Loading Using the Bootstrap Class Loader.
Loading Using a User-defined Class Loader.
Creating Array Classes.
Deriving a Class from a class File Representation.
Binding Native Method Implementations.
6. The Java Virtual Machine Instruction Set.
Assumptions: The Meaning of “Must.”
Virtual Machine Errors.
Format of Instruction Descriptions.
7. Compiling for the Java Virtual Machine.
Format of Examples.
Use of Constants, Local Variables, and Control Constructs.
Accessing the Runtime Constant Pool.
More Control Examples.
Working with Class Instances.
Operations on the Operand Stack.
Throwing and Handling Exceptions.
Compiling Nested Classes and Interfaces.
8. Threads and Locks.
Terminology and Framework.
Execution Order and Consistency.
Rules About Variables.
Nonatomic Treatment of double and long Variables.
Rules About Locks.
Rules About the Interaction of Locks and Variables.
Rules for volatile Variables.
Prescient Store Operations.
Example: Possible Swap.
Example: Out-of-Order Writes.
Locks and Synchronization.
Wait Sets and Notification.
9. Opcode Mnemonics by Opcode.
Appendix: Summary of Clarifications and Amendments.
The Java(TM) virtual machine specification has been written to fully document the design of the Java virtual machine. It is essential for compiler writers who wish to target the Java virtual machine and for programmers who want to implement a compatible Java virtual machine. It is also a definitive source for anyone who wants to know exactly how the Java programming language is implemented.
The Java virtual machine is an abstract machine. References to the Java virtual machine throughout this specification refer to this abstract machine rather than to Sun's or any other specific implementation. This book serves as documentation for a concrete implementation of the Java virtual machine only as a blueprint documents a house. An implementation of the Java virtual machine (known as a runtime interpreter) must embody this specification, but is constrained by it only where absolutely necessary.
The Java virtual machine specified here will support the Java programming language specified in The Java(TM) Language Specification (Addison-Wesley, 1996). It is compatible with the Java platform implemented by Sun's JDK(TM) releases 1.0.2 and 1.1 and the Java(R) 2 platform implemented by Sun's Java(R) 2 SDK, Standard Edition, v1.2 (formerly known as JDK release 1.2).
We intend that this specification should sufficiently document the Java virtual machine to make possible compatible clean-room implementations. If you are considering constructing your own Java virtual machine implementation, feel free to contact us to obtain assistance to ensure the 100% compatibility of your implementation.
Send comments on this specification or questions about implementing the Java virtual machine to our electronic mail address: firstname.lastname@example.org. To learn the latest about the Java 2 platform, or to download the latest Java 2 SDK release, visit our World Wide Web site at http://java.sun.com. For updated information about the Java Series, including errata for The Java(TM) Virtual Machine Specification, and previews of forthcoming books, visit http://java.sun.com/Series
The virtual machine that evolved into the Java virtual machine was originally designed by James Gosling in 1992 to support the Oak programming language. The evolution into its present form occurred through the direct and indirect efforts of many people and spanned Sun's Green project, FirstPerson, Inc., the LiveOak project, the Java Products Group, JavaSoft, and today, Sun's Java Software. The authors are grateful to the many contributors and supporters.
This book began as internal project documentation. Kathy Walrath edited that early draft, helping to give the world its first look at the internals of the Java programming language. It was then converted to HTML by Mary Campione and was made available on our Web site before being expanded into book form.
The creation of The Java(TM) Virtual Machine Specification owes much to the support of the Java Products Group led by General Manager Ruth Hennigar, to the efforts of series editor Lisa Friendly, and to editor Mike Hendrickson and his group at Addison-Wesley. The many criticisms and suggestions received from reviewers of early online drafts, as well as drafts of the printed book, improved its quality immensely. We owe special thanks to Richard Tuck for his careful review of the manuscript and to the authors of The Java(TM) Language Specification, Addison-Wesley, 1996, for allowing us to quote extensively from that book. Particular thanks to Bill Joy whose comments, reviews, and guidance have contributed greatly to the completeness and accuracy of this book.
Notes on the Second Edition
The second edition of The Java(TM) Virtual Machine Specification brings the specification of the Java virtual machine up to date with the Java(R) 2 platform, v1.2. It also includes many corrections and clarifications that update the presentation of the specification without changing the logical specification itself. We have attempted to correct typos and errata (hopefully without introducing new ones) and to add more detail to the specification where it was vague or ambiguous. In particular, we corrected a number of inconsistencies between the first edition of The Java(TM) Virtual Machine Specification and The Java(TM) Language Specification.
We thank the many readers who combed through the first edition of this book and brought problems to our attention. Several individuals and groups deserve special thanks for pointing out problems or contributing directly to the new material:
Carla Schroer and her teams of compatibility testers in Cupertino, California, and Novosibirsk, Russia (with special thanks to Leonid Arbouzov and Alexei Kaigorodov), painstakingly wrote compatibility tests for each testable assertion in the first edition. In the process they uncovered many places where the original specification was unclear or incomplete.
Jeroen Vermeulen, Janice Shepherd, Peter Bertelsen, Roly Perera, Joe Darcy, and Sandra Loosemore have all contributed comments and feedback that have improved this edition.
Marilyn Rash and Hilary Selby Polk of Addison Wesley Longman helped us to improve the readability and layout of this edition at the same time as we were incorporating all the technical changes.
Special thanks go to Gilad Bracha, who has brought a new level of rigor to the presentation and has been a major contributor to much of the new material, especially chapters 4 and 5 and the new "Appendix: Summary of Clarifications and Amendments." His dedication to "computational theology" and his commitment to resolving inconsistencies between The Java(TM) Virtual Machine Specification and The Java(TM) Language Specification have benefited this book tremendously.
Java Software, Sun Microsystems, Inc.
References--IEEE Standard for Binary Floating-Point Arithmetic, ANSI/IEEE Std. 754-1985. Available from Global Engineering Documents, 15 Inverness Way East, Englewood, Colorado 80112-5704 USA, +1 800 854 7179.
--Hoare, C.A.R. Hints on Programming Language Design. Stanford University Computer Science Department Technical Report No CS-73-403, December 1973. Reprinted in Sigact/Sigplan Symposium on Principles of Programming Languages. Association for Computing Machinery, New York, October 1973.
--Unicode Consortium, The. The Unicode Standard: Worldwide Character Encoding, Version 1.0, Volume 1, ISBN 0-201-56788-1, and Volume 2, ISBN 0-201-60845-6. Updates and additions necessary to bring the Unicode Standard up to version 1.1 may be found at http://www.unicode.org --Unicode Consortium, The. The Unicode Standard, Version 2.0, ISBN 0-201-48345-9. Updates and additions necessary to bring the Unicode Standard up to version 2.1 may be found at http://www.unicode.org