Modern Java
9 through 17+
Class-file features, library overlays, records, sealed classes, constants, and MethodHandles.
JVM in TypeScript / modern branch
Doppio Modern JVM
Run JVM bytecode in the browser, inspect Java 17+ compatibility work, and compile editable Java, Kotlin, or Scala source without leaving the page.
Source
Main.java / Main.kt / Main.scala
editable
Compiler
javac / K2JVMCompiler / scalac
on demand
Doppio
class loader / interpreter / JIT / BrowserFS
TypeScriptBring-up status
The compatibility matrix records implementation status and difficulty. Compiler smokes validate generated programs on both the host JVM and Doppio.
Kotlin compiler
2.4.0 smoke
Compiler startup, broad language constructs, reflection paths, contracts, and runtime execution.
Scala compiler
2.13.18 smoke
Compiler execution, collections, reflection, macros, package metadata, and functional APIs.