- Suppose Rectangle derives from Quadrilateral
- Rectangle more specific Quadrilateral
- Any operation on Quadrilateral can be done on Rectangle (i.e., perimeter, area)
- Suppose designing video game
- Base class SpaceObject
- Derived Martian, SpaceShip, LaserBeam
- Base function draw
- To refresh screen
- Screen manager has vector of base-class pointers to objects
- Send draw message to each object
- Same message has "many forms" of results
2004-12-28
