CSC223, Class 4: Polymorphic Candy, Continued

Admin:
* Remind: Email me when you miss class, but please don't miss class.
* Homework assignment coming at the end of class.

Overview:
* Review polymorphic candy example
* Solution one: Modify CandyMachine interface.
* Solution two: Use Java introspection.
* Solution three: Use the "Abstract Factory" design pattern
* Improving solution three with "anonymous inner classes"

Summarize polymorphic candy machine problem
* The problem:
  * We want to build many candy machines of the same type

Solution one: Rewrite the problem
* Add a "refill()" method to the CandyMachine interface.
* Positives
  * Continues to use a nice interface.
  * Pushes the problem "up" a level.
  * Models the real world well.
  * Relatively easy
* Negatives
  * May not be "efficient" (might repeat similar code) (LZ-B agrees)
  * Changing a published interface is EVIL
* Morals:
  * Take care in designing interfaces.
  * Do not change interfaces lightly.

Solution two: Use great knowledge of Java (Introspection)
* Get the class of the candy machine.
* Use that to make a new one
* Positives:
  * Doesn't change the interface.
  * Straightforward and logical: You need to know the class, so you ask it for the class.
* Negatives:
  * Harder to code.
  * Fails to work for base classes that lack zeroary constructors.
* Will it work for DoubleMachine?
  * Theoretical: DoubleMachines have no zeroary constructor, so it is likely that the getConstructor method will fail miserably.
  * Practical: Oooh, let's try it and see.

Detour: Terminology:
* Zeroary: No parameters
* Unary: One parameter
* Binary: Two parameter
* Trinary/Ternary: Three parameter
* N-ary: Lots of parameters (or unknown number) (or arbitrary number)

Solution three: Think about funcctional programming
* If we could pass (lambda () (new DoubleMachine(new GumballMachine())))
* Unfortunately, the bozos at Sun didn't think about higher-order functions (and they should have, since Guy Steele, who was on the Java design team, also designed Scheme)
* OO Solution: Factories!
  * A factory is an object whose main purpose is to build other objects.

Homework:
* For Friday: Design and implement your own thing that uses factories.
* For Monday: Look up "anonymous inner class"