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

2. Rice MBS Assignment Target Audience Length of Assignment
Students at the end of an objects-first CS2
Length of Assignment
Two milestones
Approximately 10 hours of work
Probably supported by one or two labs
The Role of Programming:
Vital skill
Should be mastered early
Usually taught imperative-first

3. Studying the Case Study
White-box Framework:
Extension by Subclassing
Re-implement as per given specs.
Pedagogy:
Modular design enables students to work on smaller pieces
Give jar files of framework to start
Students guided by unit test requirements
Exercises:
new fish, new environments
add features (e.g. breeding, eating, etc)
Re-implementation of initially supplied compiled classes.
UnboundedEnv
SimpleFish
Unit tests guide the way
Variant Environment Behavior
Variant Fish Behavior

4. Studying the Case Study
Static Behavior!
Separate the variants
from the invariants
+ void move()
Strategy Pattern
Dynamic
Behavior
Change

5. Rice MBS Assignment Milestone 1 Milestone 2 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

6. Preparation Read assignment document
Download materials for Milestone 1
milestone1.zip
Unzip into empty directory
Open DrJava
Copy your drjava.jar into the project directory

7. Configuring DrJava Add RiceMBSfw.jar file to “Extra Classpath”
Edit, Preferences, Resource Locations
Click on “Add” button
Click on RiceMBSfw.jar file and “Select”
Click on “OK” at the bottom of the dialog
Now the framework has been added and can be used without source
Make sure you run in “Full Java”

8. Running the Simulation
In the “Interactions” pane, type
java controller.MBSController
Play around with the simulation
Create new environment
Edit environment
Add fish
Run simulation

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

10. Part 1: KnightFish 3 Turn into right direction
Attempt one step forward
If blocked, done
If open, go there 3

11. Part 1: KnightFish 3 Attempt a second step Turn into right direction
If blocked, done
If open, go there
Turn into right direction 3

12. Part 1: KnightFish 3 Attempt the third and last step If blocked, done
If open, go there 3

13. Part 1: KnightFish 3 Moves almost like a knight, except… No jumping
If blocked, might stop on the way 3
Stop here
Stop here
Stop here

14. Part 1: KnightFish Complicated behavior Delegation method
Procedural programming: many nested if-statements
Delegation method
Nested visitors
Cannot forget to handle a situation (compiler error!)
Process flow diagramming
Makes designing complex algorithm a systematic process

15. Part 1: KnightFish Students do this assignment
Most of the code can be taken from existing examples
For lack of time, we will do something simpler
Fish attempts to move forward
If blocked, turn around 180 degrees
If open, go there
Open TeachFish.java in model.fish

16. Part 1: KnightFish protected void move() tryMoveFwd( , ); }
Ask local environment to move forward
protected void move()
tryMoveFwd( , ); }
new ILambda() {
public Object apply(Object notUsed) {
turnRight(Math.PI);
return null; }
Command to execute if blocked
new ILambda() {
public Object apply(Object moveCmd) {
((ILambda)moveCmd).apply(null);
return null; }
((ILambda)moveCmd).apply(null);
Tell the local environment to actually move the fish
Command to execute if unblocked

17. New fish class loaded at runtime!
Part 1: KnightFish
Compile the file
Run the simulation
Create a new environment, and edit it
Add a fish
Select “Add…”
Enter model.fish.TeachFish and hit “Create”
Click somewhere on the map
New fish class loaded at runtime!

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

19. Part 2: WrappingEnv Very similar to BoundedEnv
In BoundedEnv, the Location class computes a neighboring location by adding a direction vector to its own coordinates.
The new coordinates might be inside or outside the environment.
Can new coordinates ever be outside in WrappingEnv?
No! It wraps around!

20. If you go from 0 to the left, you end up at (width-1)!
Part 2: WrappingEnv
The leftmost x-coordinate that is still inside the environment is 0. The rightmost one is (width-1).
In BoundedEnv, the x-coordinate of the neighbor from there to the left is -1.
What’s the x-coordinate of the left neighbor in WrappingEnv?
If you go from 0 to the left, you end up at (width-1)!

21. Inheritance! Let WrappingEnv extend BoundedEnv
Part 2: WrappingEnv
The necessary changes are centralized in a single method, WrappingEnv.Location.getNeighbor.
Since BoundedEnv and WrappingEnv are so similar, what OO technique can we apply to maximize code-reuse?
Inheritance! Let WrappingEnv extend BoundedEnv

22. Part 2: WrappingEnv Need to write constructors
The framework uses factory methods
Abstract creation
To complete the environment, we have to override the factory methods
WrappingEnv.makeLocation
WrappingEnv.makeEnvFactory (code provided for makeEnvFactory)
Students’ code is still based on existing code, but cannot simply be copied and modified anymore

23. Part 2: WrappingEnv Open WrappingEnv.java in sysModel.env
The project was split into “model” and a “sysModel” packages to clearly separate system code (environments) from user code (fish)
Fish more likely to get changed than environments
Edit the WrappingEnv.Location.getNeighbor method
Students would have to do a little bit more

24. Part 2: WrappingEnv
public ASquareEnv.Location getNeighbor(Direction dir) {
double newX = getX() + dir.getDeltaX();
double newY = getY() + dir.getDeltaY();
if (newX < 0) {
newX = _width + newX; }
else if (newX >= _width) {
newX = newX - _width;
if (newY < 0) {
newY = _height + newY;
else if (newY >= _height) {
newY = newY - _height;
return makeLocation(newX,newY);

25. Part 2: WrappingEnv Compile the file Run the simulation
Create a new environment
Select “Add…”
Enter sysModel.env.WrappingEnv and hit “Create”
Pick a size and create the environment
Add fish

26. End of Milestone 1 Students submit code for Part 1 and Part 2
Material for Milestone 2 gets released after submission deadline
Contains solutions for Milestone 1