Jolang is Java transpiler and extender written on Go
Try it (transpile Java to JS)
mkdir ~/Projects
cd ~/Projects
git clone https://github.com/jolangorg/jolang
git clone https://github.com/jbox2d/jbox2d
cd jolang
# Transpile all Java files
go run github.com/jolangorg/jolang/cmd/jo \
-src="~/Projects/jbox2d/jbox2d-library/src/main/java" \
-write-all
# You can also write AST files with -write-ast flag
go run github.com/jolangorg/jolang/cmd/jo \
-src="~/Projects/jbox2d/jbox2d-library/src/main/java" \
-write-all
-write-ast
python3 -m http.server &
xdg-open http://localhost:8000/html/