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This project was submitted by Meyer Kizner, Max McCarthy, and David Xu as our final project for CIS 198 at the University of Pennsylvania in spring 2016.

Please note that because this project was completed for a course, it is not under active development. The code and documentation in this repository is available as-is, and we will not be providing support beyond what already exists here.


This project implements a considerable subset of a Java virtual machine, in accordance with the Java SE 7 specification. It consists of a parser, class loader, and interpreter, which together can be used to read an arbitrary class file (subject to certain restrictions on the Java bytecode it contains), load it (and other necessary classes from the Java runtime libraries) into an interpreter, and execute the main method.

We achieved near-completion of many of these features, but got stuck within initialization of the PrintWriter and FileDescriptor classes for the System.out.println method, since they used a number of JVM features (namely, loading the java.util.concurrent.atomic.AtomicInteger class) which we had not intended to support. For this reason, the minimum required parts of the Java Class Library (JCL) are reimplemented in the rt/ directory in terms of a RustStdout class, which calls a native method for writing to a file descriptor.

As it stands, the VM successfully executes a HelloWorld.class file. It has not been tested beyond that.

To find out more information about the project, please see and for our initial project propsoal and final report.

Running Hello World

This project is organized around a single integration test: executing a compiled "Hello, world!" program from a .class file.

Our VM does not support Java 7 and 8 features (including lambdas and the invokedynamic instruction). You will need to compile the Java source code in the rt directory targeting source level 1.6, which can be accomplished with the following command:

$ cd rt/
$ javac -source 1.6 -target 1.6

Then, run cargo test from the project root and you should see the test pass.


This software is freely available under the terms of the Apache License 2.0.


Final project for CIS 198 at Penn



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