The import button is for generated java .class  or .jar file (so called java byte code.),
It is not for java source code.

You have found a way to import java source.
But I thinj your example would not work. Because what you have imported is an applet. I do not know there is a way to add another applet inside another applet. (You can add drawingPanel inside another draeingPanel).
The java code you tried to import is a complete java applet. You can not put that inside an ejs applet.
You need to remove some of the code to make it work.

I was not able to try out your xml because you did not attach [u]Calc3.java[/u]