Software Engineering I
Notes for Sept. 9, 2013

Methods, Operations, & Polymorphism

Polymorphism - property of OO SW where an abstract operation may be performed
in many different ways.

Methods are procedural abstractions used to implement the behavior of a class

Operations (in the context of SW Eng) are higher level abstractions than 
methods and are independent of code.

Example:  Inheritance from an Account Class

           +--------------+
           | Account      |
           +--------------+
           |CalcInterest()|
           +--------------+
                  ^
                 / \
                 -+-
                  |
      +-----------+-------------------+
      |           |                   |
+-----+--------+ ++-------------+ +------+--------+
|SavingsAcct   | |CheckingAcct  | |MortgageAcct   |
+--------------+ +--------------+ +---------------+
|CalcInterest()| |CalcInterest()| |CalcInterest() |
+--------------+ +--------------+ +---------------+

Inheritance Hierarchy

Superclass - has features common to many classes to avoid duplication
Subclass - allows for specialization to divide complex functionality

Example:

common features to accounts such as open, close, deposit

Specialized features
  -Mortgage Account may need special interest function

Superclasses relationship to subclass is called generalization or parent
Subclass relationship to superclass is called specialization or child

Inheritance is the implicit possession by a subclass of all features defined
in the superclasses (parent and ancestor classes) including variables and
methods.

How does this work in Java?

Rules
  -ambiguous names often give poor generalizations
  -subclasses should be distinctive
  -all inherited features should make sense

Begin discussion of effect on inheritance hierarchies on polymorphism and 
variable declarations.