1. Nifty Assignments: Marine Biology Simulation
Eric Cheng
Mathias Ricken
Dung “Zung” Nguyen
Stephen Wong
OOPSLA ‘04 Educators’ Symposium
October 25, 2004

2. Marine Biology Simulation
Based on AP Marine Biology Simulation
Completely redone using OO design
More robust, flexible, and extensible
Two-week assignment in our objects-first CS2 courses
Requires broad range of skills
Assignment and Source Code Available

3. Marine Biology Simulation
Demo

4. Structure of the Assignment
Milestone 1
Part 1: KnightFish
Add a new fish species to the simulation
Part 2: WrappingEnv
Add a new kind of environment
Milestone 2
Part 3: Internals
Re-implement parts of the simulation framework
Part 4: Behavior Strategies
Refactor framework to allow dynamic behavior changes
Support code includes solution to Milestone 1

5. Part 1: KnightFish
Randomly pick one of 8 targets 1 2 8 3 7 4 6 5

6. Part 1: KnightFish 3 Turn into right direction For each step
If blocked, done
If open, go there and attempt the next step 3

7. Part 1: KnightFish Complicated behavior Visitor-Based Delegation Model
Procedural programming: nested if-statements
OOP: nested visitors
Visitor-Based Delegation Model
Process flow diagramming makes designing complex algorithms a systematic process
Cannot forget to handle a situation (compiler error!)

8. Part 2: WrappingEnv Grid-based, bounded, and rectangular environment
If the fish leaves on one side, it re-enters from the other side (toroidal)

9. Part 2: WrappingEnv Students learn
To reuse existing code by subclassing
To integrate new code into a framework
Students’ code still based on existing code
But cannot simply be copied and modified anymore

10. Part 3: Internals Code missing in several places of the framework
Students reimplement critical portions
Gives students a tour of the entire framework
Unit tests provide guidance
Error messages in plain English

11. Part 4: Behavior Strategies
Static Behavior!
Separate the variants
from the invariants
+ void move()
Strategy Pattern
Dynamic
Behavior
Change

12. Part 4: Behavior Strategies
Students have the opportunity to
Apply design patterns to improve the project
Refactor a substantial portion of the code
Experience how loose coupling makes this easy
Requires new design and code that augments existing framework

13. Assignments in Objects-First
Assignments have to be rich and deep
Highlight benefits of object-orientation
Large design portion
Find proper abstractions, variants / invariants
Solve family of problems
Challenge to find suitable assignments
Must be within students’ grasp
Milestone 2 due today!

14. The Culmination of a Unified OO Pedagogy
MBS
~ end of 2nd semester.
Unit Tests
Design Patterns
Polymorphism
Abstract Structure and Behavior