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The core of Java technology, the Java virtual machine is an abstract computing machine that enables the Java platform to host applications on any computer or operating system without rewriting or recompiling. Anyone interested in designing a language or writing a compiler for the Java virtual machine must have an in-depth understanding of its binary class format and instruction set. If you are programming with the Java programming language, knowledge of the Java virtual machine will give you valuable insight into the Java platform's security capabilities and cross-platform portability. It will increase your understanding of the Java programming language, enabling you to improve the security and performance of your programs.
The author employs a tutorial approach that provides a detailed look into the central workings of the technology and teaches the reader how to write real programs for the Java virtual machine. He describes methods for becoming a better programmer through an advanced understanding of the Java virtual machine and Java technology. Programming for the Java Virtual Machine offers comprehensive coverage of all the major elements of the Java virtual machine--classes and objects, control instructions, debugging, class loaders, compiling the Java programming language, performance issues, security, and threads and synchronization. The book provides an introduction to the Java Virtual Machine Specification (JVMS), with a collection of topics that help programmers understand the Java virtual machine and the JVMS better. In addition, the book features implementations of Prolog and Scheme, a language that runs on top of the Java virtual machine, generating Java virtual machine code as it runs and using a Java virtual machine class loader to load the generated code into the system.
You will find detailed information on such topics as:
Numerous examples illustrate techniques and concepts, and exercises with solutions help you gain practical experience.
1. Introduction to the Java Virtual Machine.
Java Virtual Machine and Java.
What Is the Java Virtual Machine?
class File Format.
Organization of the Java Virtual Machine.
Native Method Stacks.
Timing of Garbage Collection.
Versions of the Virtual Machine.
Future of the Java Virtual Machine.
.class and .super Directives.
Structure of an Oolong Program.
Defining the Class.
Mnemonic Naming Conventions.
Testing Code Examples.
Small Constants and null.
Local Variables as Method Arguments.
Nonnumbers and Infinity.
Floating-Point Arithmetic and strictfp.
Widening and Narrowing.
Arrays of Numbers.
Just Biding Your Time.
What Is an Object?
Objects and References.
Types and getfield.
Changing Field Values.
Invoking Methods on Objects.
Method Inheritance and Overriding.
Overloading and Method Matching.
Invoking a Method Directly.
invokespecial and super.
Casting, Fields, Methods, and Java.
Static Fields and Methods.
Arrays of Reference.
Length of Arrays.
Multiple Exception Handlers.
Other Ways to Throw Exceptions.
A Gentler Way of Checking Type.
How the Verification Algorithm Works.
Is It a Structurally Valid class File?
Are All Constant References Correct?
Will Each Instruction Always Find a Correctly Formed Stack and Local Variable Array?
Example 1: Hello, World.
Example 2: gotos and ifs.
Example 3: Code That Doesn’t Verify.
Example 4: Dealing with Subclasses.
Do External References Check Out?
Java Language and Verification Algorithm.
Fooling the Virtual Machine with a Java Compiler.
Other Languages and the Verification Algorithm.
Other Safety Requirements.
Debugging Directives in Oolong.
.source Directive and .line Directives.
Debugging Oolong Programs.
How Classes Are Loaded.
Loading Classes without a Class Loader.
Making Your Own Class Loader.
Working with Class Objects.
class File Header.
Field, Method, and Class Entries.
Fields and Methods.
Expressions and Statements.
Expression Result Types.
Compile-Time Types and Type Restrictions.
Type Safety and Verifiability.
Compiling Statements and Expressions.
Local Variable Declarations.
Fields and Variables.
Assignments as Expressions.
Type-Checking in Assignments.
Creating New Objects.
Class Name Abbreviations.
Casting Numeric Values.
Virtual Method Calls.
Static Method Calls.
Example of Method Calls.
Expressions as Statements.
Ifs and Booleans.
Floating-Point Comparisons and NaN.
References and Object Equality.
Other Control Structures.
Compiling Control Constructs.
Compound Statements and Verification.
Using Other Constructors in the Same Class.
Field Initializers and the Constructor.
Java Version 1.1.
Variable Scoping with Inner Classes.
Iterators in Sather.
Iterators with Arguments.
Implementing Parameterized Types with a Generic Class.
Implementing Parameterized Types as Templates.
Interfaces for Multiple Inheritance.
Implementing the Interfaces.
Compiling Scheme into Bytecodes.
Compiling Lambda Expressions.
Using Local Variables.
Using Type Information.
Introduction to Prolog.
Binding Patterns and Implications.
Facts as Rules.
More About Unification.
Rules as Programs.
yield and Backtracking.
Fast Virtual Machines.
Garbage Collection Performance.
Bytecode Optimization Techniques.
Java platform and Need for Security.
Security Promises of the JVM.
Security Architecture and Security Policy.
Basic Applet Security Policy.
More Sophisticated Policies.
Some Potential Attacks.
Protecting the Security Manager.
Bypassing Java Security.
Using Unconstructed Objects.
Changing the Class of a Reference.
Reading Uninitialized Fields.
Array Bounds Checks.
Example: Multithreaded Web Server.
Exceptions and Threads.
Sharing State Between Threads.
Need for Synchronization.
Exception: longs and doubles.
Monitors and Object Locks.
Synchronization in Java.
Surrendering Control of the CPU.
Waiting for Another Thread.
Instructions by Opcode.
Instructions by Category.
Data Type Conversion.
Using the Oolong Assembler.
Instructions with No Arguments.
Fields and Methods.
ldc, ldc_w, and ldc2_w.
Every time you compile a Java program to produce a
class file, you've written a program for the Java virtual machine. This book is designed to take you to the next level: writing Java virtual machine (JVM) programs directly, without the aid of a Java compiler. A number of people would want to do this:
Advanced Java programmers want to know how the JVM works, in detail. Learning the details of the JVM will help improve your understanding of what a Java program does. Some messages from the JVM will be clearer after you understand how the JVM looks at your program. This understanding can also help you improve the performance of your programs.
Another reason for advanced Java programmers to learn JVM programming is that it will help you understand how JVM code moves. One of the most important uses of Java is to download applets from the Internet (or other sources). The JVM uses a class called
ClassLoader to incorporate code from the Internet into the JVM. The
ClassLoader has many other uses. The Java Foundation Classes use subclasses of
ClassLoader to load new Look and Feel classes. Some databases use other subclasses of ClassLoader to incorporate queries written in Java directly into the database.
Security experts already know that the Java language is designed with security features in mind. Java promises to allow users to download applets from the Internet without fear. However, these promises seem empty until you know precisely how the JVM keeps the promises Java makes. This book discusses in detail how the JVM verification algorithm works. Knowing the verification algorithm will give you greater confidence in the security of the JVM.
This book will give you the tools you need to build your own secure systems on top of the JVM, by explaining both what promises the JVM makes (and how it keeps them) and what promises it doesn't make.
Language designers want to design new languages for the Java virtual machine. Although the Java language is excellent, perhaps the best general-purpose programming language ever created, there are still times when a different language does the job better. Sometimes these are general-purpose languages built into an application (like WordBasic in Microsoft Word or Emacs Lisp). Others are tiny, special-purpose languages (like SQL, regular expressions, or filters in PhotoShop).
This book describes compilers for two languages, Scheme and Prolog, which are very different from Java. These compilers generate JVM code and use a subclass of ClassLoader to load it into the system. By compiling into JVM code, these non-Java languages gain some of the "Write Once, Run Anywhere" properties of Java without losing the power of the original language. These compilers can be used as a starting point for compiling other languages. Other languages already implemented for the JVM include Tcl, ML, Eiffel, Python, and Ada.
As more and more programs are written in Java, there is an increasing need to implement new languages. By implementing these languages using the JVM, you can get the portability and performance of the JVM.
This book assumes that you have a good basic knowledge of Java. Many of the ideas in the book are explained in terms of Java; at the same time, the book tries to explain Java in terms of the JVM. Hopefully, this will reinforce your understanding of both the Java language and the Java virtual machine.
If you're new to Java, let me recommend The Java Programming Language, by Ken Arnold and James Gosling. It's an excellent introduction to the language written in part by the originator of Java himself, James Gosling.
Many sections have exercises. The exercises don't introduce new material, but they do reinforce the existing lessons. Most of the exercises ask you to write small pieces of code. For some exercises, answers are provided at the back of the book. If you're using this book for a class and you've been assigned the exercises as a homework problem, then turning in the answers at the back of the book is cheating! Fortunately, real JVM programmers are trustworthy.
This book has been designed to stand on its own. You should be able to read it without owning any other books on Java. However, there are two books which you may find very useful.
One is The Java Virtual Machine Specification (JVMS), by Frank Yellin and Tim Lindholm. It is the "truth" of the Java virtual machine. All JVM implementers, including Sun itself, are expected to adhere to the definition of the Java virtual machine contained in the JVMS. Wherever your JVM implementation disagrees with the JVMS, it is always the JVMS that is correct. I recommend that you have a copy on hand if you want to do a lot of JVM programming, because it is the final word on any JVM-oriented question.
Another book I recommend is The Java Language Specification, by James Gosling, Bill Joy, and Guy Steele. This is a large, thick tome that contains the absolute truth about the Java language. It does an excellent job of specifying all the details of what a Java program means. It is meticulously precise, but it can still be a lot of fun to read because it throws in many funny examples and quotes. Even just browsing the index can be a treat. (Look up the index entry for prime numbers to see what I mean.)
Both of these books are available over the Internet at http://java.sun.com/docs. Paper copies are available at any bookstore.
While you're on the Internet, let me recommend one other source of information. The newsgroup
comp.lang.java.machine is dedicated to discussing how the Java virtual machine works, how it is implemented, and so forth. I'm a frequent reader and contributor, and there are many other experts willing to share their copious knowledge.
I would like to thank Stefan Gower for giving me the original idea of implementing a Scheme compiler for the Java virtual machine. Christopher Cook, William Andersen, Brian Peterson, and Paul Brinkley were indispensable, allowing me to explain JVM concepts to them until I finally found a lucid explanation.
Marina Lang at Addison Wesley Longman was instrumental in guiding me through the process of getting a book written. Thanks also to the many reviewers she found who helped me turn drafts into something readable.
Finally, I would like to thank the regular posters to
comp.lang.java.machine, the newsgroup for the JVM. They provided answers to a lot of questions and brought up questions I had not previously considered.
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