Rust JVM

A far-from-complete Java Virtual Machine written in Rust

What is supported

This JVM implements most bytecode instructions. Their implementation may however not be complete as it has been tested with a limited number of classes. Moreover, the JVM's native class support stays limited. The files in the java folder show what is currently being supported:

• Hello.java: basic Hello World
• Arithm.java: simple integer arithmetic
• Mandelbrot.java floating-point calculations
• Streams.java: a Java streams example using map(), filter() and forEach()
• Person.java, AgeRange: class, switch statements and enums
• TestThread.java, RunnableDemo.java: multi-threading
• Exceptions.java: exception handling

See also the following to understand more about Java/Scala/Kotlin code gets converted into bytecode instructions:

• Bytecode overview
• Java Streams overview
• The Java switch statement
• Java enums
• Compiling bytecode into assembly

How to use it

The main use is to run jvm <class name> (the corresponding .class file must be in the current directory or in the Java directory). It is also possible to pass a debugging level (from 1 to 3) to get more information about the bytecode both defined in the .class file and the bytecode instructions actually executed.

> cargo build
   Compiling jvm v0.1.0 (/Users/user/JVM)
    Finished dev [unoptimized + debuginfo] target(s) in 1.69s

> cargo build --release
   Compiling jvm v0.1.0 (/Users/user/JVM)
    Finished dev [optimized] target(s) in 5.32s

> ./target/debug/jvm Arithm 43
Convert 43 into 21

> ./target/debug/jvm -d 1 Hello
Executing method main
Execute 0       getstatic java/lang/System out Ljava/io/PrintStream;
Execute 1       ldc "Hello, World!"
Execute 2       invokevirtual java/io/PrintStream.println(Ljava/lang/String;)V
Hello, World!
Execute 3       return

> ./target/debug/jvm Person
John Smith
Can legally drink (in the U.S.)
Young Adult
Will or Kevin?

> ./target/debug/jvm Streams Alice Bob Charlie Anna Delta
alice
anna

> ./target/debug/jvm TestThread
Creating Thread-1
Starting Thread-1
Creating Thread-2
Running Thread-1
Starting Thread-2
Thread: Thread-1, 4
Running Thread-2
Thread: Thread-2, 4
Thread: Thread-1, 3
Thread: Thread-2, 3
Thread: Thread-1, 2
Thread: Thread-2, 2
Thread: Thread-1, 1
Thread: Thread-2, 1
Thread Thread-1 exiting.
Thread Thread-2 exiting.

> ./target/debug/jvm Exceptions 123 0
Exception caught with the following stack trace:
Exception in java/lang/ArithmeticException: / by zero
        at Exceptions.operation(Exceptions.java:15)
        at Exceptions.main(Exceptions.java:27)

> ./target/release/jvm Mandelbrot
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