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In the class hierarchy as developed so far, each class
exhibits only a default constructor. When you create an object in such a
hierarchy, all the
default constructors in the object's class and
superclasses are called automatically, and each has the opportunity to
contribute to the values of the member variables associated with the new
object. In particular, the default constructors in all the box_car
class and all superclasses of the box_car class are called whenever
a box_car object is created:
*--------------------*
| container |
*--------------------*
^
|
*--------------------* *--------------------*
| box | | railroad_car |
*--------------------* *--------------------*
^ ^
| |
| *--------------------*
| |
*---------*
| box_car |
*---------*