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

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 http://www.owlnet.rice.edu/~comp202

Marine Biology Simulation Demo

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

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

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

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!)

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

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

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

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

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

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!

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