Since Java 1.6 the JVM can run a myriad of programming languages on top of instead of just Java. I conceptually understand how Java is run on the Java VM, but not how other languages can run on it as well. To me, it all looks like black magic. Do you have any articles to point me to so I can better understand how this all fits together?
JVM – How Does the Java Virtual Machine Execute Code in Other Languages?
jvm
Best Answer
The key is the native language of the JVM: the Java bytecode. Any language can be compiled into bytecode which the JVM understands - all you need for this is a compiler emitting bytecode. From then on, there is no difference from the JVM's point of view. So much so that you can take a compiled Scala, Clojure, Jython etc. class file and decompile it (using e.g. JAD) into normal looking Java source code.
You can find more details about this in the following articles / threads:
I am not aware of any fundamental changes in the Java 5 or 6 JVMs which would have made it possible or easier for (code compiled from) other languages to run on it. In my understanding, the JVM 1.4 was more or less as capable in that respect as JVM 6 (there may be differences though; I am not a JVM expert). It was just that people started to develop other languages and/or bytecode compilers in the first half of the decade, and the results started to appear (and become wider known) around 2006 when Java 6 was published.
However, all these JVM versions share some limitations: the JVM is statically typed by nature, and up to release 7, did not support dynamic languages. This has changed with the introduction of
invokedynamic, a new bytecode instruction which enables method invocation relying on dynamic type checking.