Java programs compile into Java bytecode. Java bytecode executes in the Java Virtual Machine, a runtime environment that compiles that bytecode further into machine code, and optimizes the runtime by identifying “hot” code paths and keeping those hot code paths executing quickly.

The Java Virtual Machine is a popular platform for building languages on top of. Languages like Scala and Clojure compile down to Java bytecode, and can take advantage of the garbage collection system and the code path optimizations of the JVM. But when Scala and Clojure compile into Java bytecode, the code “shape”–the way that the programs are laid out in memory–is not the same as when Java programs compile into Java bytecode. Executing bytecode that comes from Scala will have certain performance penalties relative to a functionally identical program written in Java.

GraalVM is a system for interpreting languages into Java bytecode that can run efficiently on the JVM. Any language can be interpreted into an abstract syntax tree that the GraalVM can execute using the JVM. Languages that can run on GraalVM include JavaScript, R, Ruby, and Python.

Thomas Wuerthinger is a senior research director at Oracle and the project lead for GraalVM. He joins the show to explain the motivation for GraalVM, the architecture of the project, and the future of language interoperability. It was an exciting discussion and I learned a lot about the Java ecosystem.

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