Nifty Assignments: Marine Biology Simulation

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Nifty AssignmentsMarine Biology Simulation

• Eric Cheng
• Mathias Ricken

Dung Zung Nguyen Stephen Wong
OOPSLA 04 Educators Symposium October 25, 2004
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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

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Marine Biology Simulation
Demo
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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
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Structure of the Assignment
White-box Framework Extension by Subclassing
Variant Fish Behavior
Variant Environment Behavior
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Part 1 KnightFish

• Randomly pick one of 8 targets

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2
3
8
4
7
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Part 1 KnightFish

• Turn into right direction
• For each step
• If blocked, done
• If open, go there and attempt the next step

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Part 1 KnightFish

• Moves almost like a knight, except
• No jumping
• If blocked, may stop on the way

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Stop here
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Part 1 KnightFish

• Complicated behavior
• 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!)

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Part 2 WrappingEnv

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

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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

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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

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Part 3 Internals

• Students gain insight into
• Abstraction and loose coupling
• Message passing
• Writing large frameworks
• Working with someone elses code
• Requires extensive work within existing framework

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Part 4 Behavior Strategies

• Once students have understood the existing
  framework, they can improve it
• Point out one of the flaws
• Fish cannot change behavior
• This part involves refactoring the old code and
  creating a new class hierarchy

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Part 4 Behavior Strategies
Static Behavior!
Separate the variants from the invariants
Strategy Pattern
Dynamic Behavior Change
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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

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Summary

• Students slowly gain experience with the
  framework
• Parts 1 and 2 provide a lot of support
• Part 3 gives students more responsibility, but
  unit tests provide guidance
• Part 4 gives students freedom to design and
  improve
• Compelling and entertaining example of
  object-oriented design

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Niftiness

• Large, non-trivial project
• Focus on the design of OO systems
• Flexible yet secure design
• Can be used for other applications, e.g. OS
• Test-driven development
• Provides feedback, but not the answer

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Niftiness

• Requires broad set of skills

• Inheritance, delegation
• Unit testing
• Reading and writing documentation

• Design patterns
• Refactoring
• Components and frameworks

• Flexibility and extensibility reinforce power of
  OO design
• Entertaining, visual project

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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!

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