Observer Pattern

Examples
- Weather data
  - Illustrate the "bad choice"
- Newspaper publish/subscribe idea
- How to represent this in code?

Design Principle: Stive for loosely coupled designs between objects
that interact.
- That is, the objects are somewhat independent, but communicate now
and then.  Loose coupling allows what those objects do precisely to
change more easily.

First solution to weather station stuff:
- What about the way in which we're passing the data as arguments to
the update method?
- Subject pointer in observer: if update() passes the data, why do we
need this?  ANS: to unregister later.
- How could we make WeatherStation and WeatherData observers?

Push/pull of state
- Pull: have separate getter methods.  If we add new state, old code
unchanged.

java.util.Observable
- Show Javadoc
- Draw picture
  - setChanged vs. not having it
  - how would you use it?  They wave their hands for the weather
    station, so how would you actually do it?
- How could we change Observable and Observer to use generics?  Why do
  you think that the Java library writers didn't do this?

- Swing example

- Bullet points on p. 74