Remember, you never directly write an object. You write a class,
from which an object is instantiated.
behavior: all objects that are instances of the same class
share the same behavior. That is, they have the same methods that
can be called. This is what comprises behavior.
state is the value of the instance fields of the object. With
proper encapsulation procedures, these should only be changed by methods.
identity distinguishes one object from another.
When designing an object oriented program, think of nouns as the classes,
and verbs as the methods in those classes.
Example: Car, a noun, could be a class. Move and stop, two verbs,
could be two methods of that class.