- inheritance
  - use to design 2+ entities that are different but share many common features
    1) superclass/ancestor/base class
       - class w/ common features
       - cannot refer to items defined in subclass
    2) subclass/descendant/derived class
       - extension of common class
       - inherits all attributes of common class
       - can refer to items defined in superclass
- hierarchy
  - subclass is superclass of other classes
- powerful: develop complex programs efficiently and elegantly

Quick Check:
1. B is the superclass; A is the subclass.
2. 
   ___
  |   |
  | B |
  |___|
    ^
    |
   ___
  |   |
  | A |
  |___|

3. Superclass = base class    = ancestor
   Subclass   = derived class = descendent
4. Animal and Mammal will both be superclasses.
5. Note: the arrows are meant to be solid lines.
                  _________
                 |         |
                 | Vehicle |
                 |_________|
                  ^   ^   ^
                 /    |    \
                /     |     \
               /      |      \
              /       |       \
             /        |        \
            /         |         \
 __________/_   ______|_____   __\______
|            | |            | |         |
| Motorcycle | | Automobile | | Bicycle |
|____________| |____________| |_________|
                  ^      ^
                 /        \
           _____/______   _\_____
          |            | |       |
          | Sports Car | | Sedan |
          |____________| |_______|