Other Java 16

I am using Java 16 (openJdk16)

If I create an non-ui program it compiles fine and works.

If I create a UI program it fails to compile (even though the paths are the same) with the error

src\b4j\example\main.java:7: error: package javafx.application does not exist
public class main extends javafx.application.Application

Click to expand...

Unless I add the following line


Just wondering why ?