Heyy, empty HelloWorld classfile! It is first empty file in the project. So, here is a story :

A curious child asked his mother: “Mommy, why are some of your hairs turning grey?”

The mother tried to use this occasion to teach her child: “It is because of you, dear. Every bad action of yours will turn one of my hairs grey!”

The child replied innocently: “Now I know why grandmother has only grey hairs on her head.”
Empty Machine class
isOn status, property for machine template
Machine methods -  turn On/Off, boolean isOn status
Empty Printer classfil
Printer class, with all methods
little fix, Printer was not imported to HelloWorld.java class
trying to make conflict