244: Mainline

As a general rule, you should place instance variables and define methods such that two criteria are satisfied:

• There is no unnecessary duplication of instance variables or method definitions.
• Each method defined in a class is useful in all that class's subclasses.

For example, the fCalories, cCalories, and pCalories instance variables are all placed in the Food class, because they are useful for all Food subclasses, although they are not useful for classes that are not Food subclasses, such as the Integer, Float, and Fraction classes. Similarly, various accessors and the tCalories method are defined for the Food class, because they are useful for all Food subclasses.