Use javac directly, in a recent JDK, to compile lots of files at once (i.e. one invocation of javac to compile multiple files) and you'll see. The speed is over 100,000 lines/sec: https://mill-build.org/blog/1-java-compile.html

Seriously a need for a new build tool in Java that doesn't fuck around too much.

Check out mill from the link. It’s quite good.

Oh sweet. Former Java dev turned Go dev like a decade ago, this looks close to what I want.

100% this. Ant was bad in many ways, but at least it was lightning fast. Gradle is just tragic.

Try mill from the link! https://mill-build.org/mill/index.html