1. Marine Biology Simulation Part I: Introduction
Dung “Zung” Nguyen
Mathias Ricken
Stephen Wong
TeachJava 2004!
June 25, 2004

2. The Role of Programming
Important skill
Should be taught early in a student’s career
Usually taught imperative-first
Concentrates on language elements like expressions, operators, functions, pointers…
The Role of Programming:
Vital skill
Should be mastered early
Usually taught imperative-first

3. Problems Teaching Imperative-First
Focus on syntactical elements
Exercises too simple to be motivating
Too little emphasis on design
Biased against students without prior knowledge
Problems Teaching Imperative-First:
Focus on syntax
Bias against students without prior programming experience
Oversimplifies programming
Little focus on design, documentation, testing
Not motivation

4. Object-Orientation Beneficial to software quality
Correct, robust, flexible, and extensible
Extensively covers software design
Examples are more challenging and motivating
Usually considered “advanced concept”
Objects-First
Beneficial for software quality
Covers more topics: design, implementation, testing, documentation
More complex examples

5. Assignments Assignments have to be complex Large design portion
Highlight benefits of object-orientation
Large design portion
Find proper abstractions, variants / invariants
Solve family of problems
Challenge to find suitable assignments
Example: Marine Biology Simulation

6. AP Marine Biology Simulation
Case studies in AP curriculum since 1994
Argument:
“Some good reasons to use a case study in AP Computer Science include:
Working with a program of significant length
Thinking through issues of good program design
Learning from an expert programmer”
(AP Marine Biology Simulation Case Study – Teacher’s Manual)

7. AP Marine Biology Simulation
Goal:
“Through the AP Marine Biology Simulation Case Study, the strategies, vocabulary, and techniques of object-oriented design will be emphasized.”
(AP Marine Biology Simulation Case Study – Teacher’s Manual)
Shortcomings
Improper abstractions, incorrect delineation of responsibilities
Tight coupling
 not robust
 not flexible and extensible

8. AP Marine Biology Simulation
Demo

9. AP Marine Biology Simulation
a few pitfalls...
Insecure architecture
Replicated data
Unenforceable contracts
Limited extensibility
Key issue:
Tight Coupling

10. X X X Which is not the same as here. On some global coordinate grid?
And not the same as here either.
Where am I?
I know where I am: right here.
Think Simple.
Do I know my own coordinates?
Does anyone else know my coordinates?
Should I know anyone else’s coordinates?
Do I really care where Greenwhich is?
To change my location
is to change my
LOCAL environment.
Knowing my location
does NOT mean I know
my global coordinate! ? X X X
Latitude = 29.65
Longitude = 95.28

11. Each fish has its own local environment
The local environment is an indirection layer between the fish and the global environment. X X X X X
The local environment decouples
the fish from the global environment.

12. Fish and their Environment
The local environment provides services to the fish
A fish has a local environment
Local environment communicates with global environment but fish do not.
The local environment is instantiated by the global environment
The local environment does NOT provide x-y coordinates!
Factory Method Design Pattern
Decoupled, robust & secure behavior!

13. X The fish responds accordingly! Send commands to local environment
Unblocked case command
A Fish’s Dilemma
The appropriate command is selected
Blocked case command
Can I move forward?
Send a message to the local environment! ?
Unblocked!
Blocked! X

14. A fish can ONLY move as prescribed by its environment!
Local environment makes a move command
Move command sent to fish
If desired, fish applies move command
Or…
The appropriate command is selected ?
A fish can ONLY move as prescribed by its environment! X
Move Command
Unblocked!
Blocked!

15. A fish does not need to know its x-y coordinate!
A fish does not need to know “how” to move!
Decoupled, yet
interactive behavior!
A fish is decoupled from the global environment!

16. Fish-Environment Interaction
Delegate to the local environment
SimpleFish Class
new ILambda() {
public Object apply(Object notUsed) {
turnRight(Math.PI);
return null; }
_localEnv.tryMoveFwd(this, , );
Command to execute if blocked
new ILambda() {
public Object apply(Object moveCmd) {
((ILambda)moveCmd).apply(null);
return null; }
Command to execute if unblocked

17. Fish-Environment Interaction
Depending on whether the new local environment is empty or not…
Fish-Environment Interaction
Make local environment in the direction the fish wants to move
LocalEnvironment Class
public Object tryMoveFwd(AFish f, ILambda blocked,
ILambda unblocked) {
ILocalEnv le = makeMoveFwdLocalEnv();
return le.execute(new ILocalEnvVisitor() {
public Object emptyCase(ILocalEnv h, Object nu) {
ILambda moveCmd = new MoveLambda(le);
return unblocked.apply(moveCmd); }
public Object nonEmptyCase(ILocalEnv h, Object nu) {
return blocked.apply(null);
}, null);
… either make a command that actually moves the fish…
… and execute the unblocked command
… or execute the blocked command
No if-statements!

18. Design Benefits Decoupled, abstract design Enhanced capabilities
Replaceable environments
Different fish
Robustness

19. Rice Marine Biology Simulation
Demo

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

21. Problems Using This in AP Classes
Defined curriculum
Students must perform well in exams
Teach what exams require
Current curriculum disagrees with our approach
Rice MBS is for university-level classes

22. Results Objects-first is programming for everyone
Addresses problems of imperative-first
Focus on design
Motivating assignments
Not biased against
Lack of experience
Gender
Declared Major
Year in School
SAT Scores
AP curriculum will hopefully change

23. Future Work Make simulation deadlock-safe
Extra credit competition using MBS
Game of life, outbreed other species?
Study MBS along several cognitive dimensions
Improve assignment quality