WOW! Hmm, I think you may be using the same book as us for your class. I have seen the Coin class before, we used this exact code in an example program last week.
I am still not sure if I understand the problem. Please correct me if I am wrong, but I am thinking that the coin and dart class need to be modified to include the .value method sence this method is refrenced in the Interface_value_use.java code.
Do you have a TA handy that you can ask for a clearer explaniation of the problem that needs to be addressed? I will help you in any way I can because I think it will help me understand classes better, but I dont fully understand what the problem is asking.
It is also kind of interesting to see that your school uses the Keyboard class. Our instructor doesnt use the keyboard class because it is not a standard Java class.