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Preface
This document describes version 1.0 of the Java Virtual Machine and its instruction set. We have written this document to act as a specification for both compiler writers, who wish to target the machine, and as a specification for others who may wish to implement a compliant Java Virtual Machine.
The Java Virtual Machine is an imaginary machine that is implemented by emulating it in software on a real machine. Code for the Java Virtual Machine is stored in .class files, each of which contains the code for at most one public class.
Simple and efficient emulations of the Java Virtual Machine are possible because the machine's format is compact and efficient bytecodes. Implementations whose native code speed approximates that of compiled C are also possible, by translating the bytecodes to machine code, although Sun has not released such implementations at this time.
The rest of this document is structured as follows:
- Chapter 1 describes the architecture of the Java Virtual Machine.
- Chapter 2 describes the
.class file format.
- Chapter 3 describes the bytecodes.
- Appendix A contains some instructions generated internally by Sun's implementation of the Java Virtual Machine. While not strictly part of the specification we describe these here so that this specification can serve as a reference for our implementation. As more implementations of the Java Virtual Machine become available, we may remove Appendix A from future releases.
Sun will license the Java Virtual Machine trademark and logo for use with compliant implementations of this specification. If you are considering constructing your own implementation of the Java Virtual Machine please contact us, at the email address below, so that we can work together to insure 100% compatiblity of your implementation.
Send comments on this specification or questions about implementing the Java Virtual Machine to our electronic mail address: java@java.sun.com.
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