CSC152 2005F, Class 28: Parameterized Classes II : A Review of Polymorphism

Admin
* Kudos to Jacob
* Sorry that this topic is taking longer than I planned, but I think it's better to go through stuff carefully and make sure you understand it.
* Sorry for the confusion at the end of last class; believe it or not, but we did get the results I was expecting, just not in the form I expected.

Overview
* Generalizing our solution, revisited.

Status:
* Wrote expt2
* Trying to generalize using interfaces

Using Interfaces and Polymorphism
* Situation: 
  * You have a method, m, that operates on one class, c, of object
  * You want to make it operate on similar objects in class d.
* Preparatory thinking
  * Determine which of the original objects's methods you rely on
    * In expt2, we rely on a constructor and on multiply
  * Decide whether or not methods with the same name and semantics can be expected in all similar classes (if not, this technique probably won't work)
    * BigIntegerVariable: check
    * DecimalVariable: check
    * StringVariable: Um ... what does it mean to multiply or exponentiate a string?  No.
    * Rabbit: Check
* Programming
  * Devise an interface, i, that lists the methods m depends on.
    * May need a hack for constructors
  * Update m to use i in place of c.
  * Indicate that your original class (c) implements i
  * Make any changes necessary to ensure that the previous indication is correct
  * Test
  * Indicate that your new class (d) also implements i
  * Make any necessary changes
  * Test