CSC207.01 2014S, Class 24: Java Generics
========================================

_Overview_

* Preliminaries.
    * Admin.
    * Questions.
* Topics.
    * Homogenous vs. heterogenous collections.
    * Writing general code with type variables.
    * Java's generics.
    * Generic classes, interfaces, and methods.
    * Handling multiple types.
* Lab.

Preliminaries
-------------

### Admin

* Have fun with Earnest!
* Note that I talked a bit about program design at yesterday's extra.
  The eboard is posted.
* Homework 5 is due March 5.
* The exam makeup is due Sunday at 10:30 p.m.  There will be no extensions.
* Extra credit: 
    * Harris wellness thingy tonight
    * Galaxy dinner and auction tonight
      <http://www.galaxyinc.org>
    * Convocation next Wednesday.
    * Grinnell image presentations next Thursday and Friday.

### Questions

_How do we arrive at the invariant for the "Dutch National Flag" problem?_

> There's no particular strategy for arriving at invariants.  It's like
much of algorithm design: You think about the problem for awhile.
In the case of invariants, the idea is that once you've *started*
to design an algorithm, you have a model for the state of the system.
The invariant represents that state.

> In this particular case, I expect that midway through the algorithm, I'll
have a section of red values, a section of white values, a section of
blue values, and a section of unknown values.

_In part D, I'm not sure about "one of which only takes on values of
x^2^k". I think it should be "x^(2k)", not "x^2^k"._

> x^2^k is x^(2^k) and not (x^2)^k.  And that's what I've written.
Exponetiation is right-associative.  And I do intend that it be
"x to the powers of two".  But that may not be the best invariant for
you; it's just how I find it useful to think about the problem.

> xk+1 = x * xk, for even k >= 0. I think you mean "every", not even._

While it's try for every k, I do mean "for even k", because I only want
this rule to apply to odd exponents.

Homogenous vs. heterogenous collections
---------------------------------------

Writing general code with type variables
----------------------------------------

Generic classes, interfaces, and methods
----------------------------------------

Handling multiple types
-----------------------