Yeah javac is pretty great. I was doing Kotlin for some time and I was getting very annoying by how much slower and slower running tests and doing full builds became. I thought it was some issue with the JVM ecosystem. Then I started a project with pure Java and I was blown away by how fast it was. Unit tests in my IDE running as fast as I'm used to in Go. And indeed I was surprised by the speed of the compilation step of the build too. Perhaps Kotlin is doing better now, haven't touched it in a few years, but yeah, Java made some great steps there in the past decades.