[Java-gnome-developer] Gdk classes not found

[Happy <hap...@gm...>]

Hi,

import org.gnome.gdk.EventExpose;
import org.gnome.gdk.Color;

These and many other gdk classes cannot be found.

javac -classpath $CLASSPATH:/usr/share/java/gtk4-1.jar $1.java

Ubuntu 17.10 / 64 bit

For example used in EnterNotifyEvent 
http://zetcode.com/gui/javagnome/events/

Thanks,