My crack at a JVM implementation in Java.
Functionality supported so far:
- Synchronization & multithreading
- File I/O (including zip files, reading from stdin etc)
- Garbage collection
Still to come:
- Socket I/O
- JMX
- More reflection methods
The JVM is written in Java 8 but runs Java 7 code.
This JVM has only been confirmed to work when run by the Oracle HotSpot JVM bundled with JDK 8 on OSX. It is unlikely to work on any other platform!
To try the demo and see the JVM in action, take the following steps:
- make sure you have the full Java 7 SDK downloaded and installed
- set the JAVA_7_HOME environment variable to point to the Home directory of your Java 7 install
- clone the repo
- run mvn clean install in the root directory. This will build the core jar (as well as confirming that the JVM will run on your platform)
- cd demo
- mvn assembly:single - this will build the demo jar
- cd target
- unzip jvm-demo.zip
- cd jvm-demo/jvm-cp
- javac Demo.java - compile the demo code
- cd ..
- ./javaJvm Demo
The provided Demo.java uses a Scanner to read from System.in and prints the reversed input. You can write your own demo code, just replace 'Demo' with 'YourClass' in the instructions above.
In a separate window you may wish to run tail -f jvm.log to see what the JVM is up to.
To vary the output in the log file, change the log level in lib/logback.xml
| Level | Output |
|---|---|
| WARN | See when GC is running |
| INFO | See method invocations |
| DEBUG | See individual opcode executions |
Please get in touch if you discover any bugs or have any issues running the demo!