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243: Mainline 
 

To gain insight into how classes, instance variables, and methods 
work together, you should draw a class-hierarchy diagram, such as 
the following: 

*--------------------------------------* 
| Object                               | 
*--------------------------------------* 
  | 
  | subclass 
  v 
*--------------------------------------* 
| Food                                 | 
|  Instance variables   Methods        | 
|    fCalories            fCalories    | 
|    cCalories            fCalories:   | 
|    pCalories            cCalories    | 
|                         cCalories:   | 
|                         pCalories    | 
|                         pCalories:   |  
|                         tCalories    |                 
|                         isVegetable  | 
*--------------------------------------* 
  |   |   | 
  |   |   | subclass 
  |   |   *-----------------------------------------------------* 
  |   | subclass                                                | 
  |   *--------------------------*                              | 
  | subclass                     |                              | 
  v                              v                              v 
*----------------------------* *----------------------------* *--- 
| Vegetable                  | | Dairy                      | |  
|             Methods        | |                            | | 
|               isVegetable  | |                            | | 
*----------------------------* *----------------------------* *-- 
  |                 |  |  |       |  |  |  | 
  | instance        |  |  |       |  |  |  | 
  v                 v             v  v 
*--------------*   Other         Various 
| a Vegetable  |   Vegetable     Dairy 
*--------------*   instances     instances 

 
Such a class-hierarchy diagram helps you to see how to distribute instance 
variables and methods among the classes in the hierarchy.