Marine Biology Simulation Case Study

1. Marine Biology SimulationCase Study Alyce Brady Kalamazoo College

2. Case Study as Educational Tool • describes a real situation • provides an interesting example from which to draw certain lessons • provides a context for comparing theoretical ideas against real-world experience

3. Case Studies in AP CS • try to give the illusion of being a real-world situation (MBCS) or real-world tool (BigInt) • must be simplified and cleaned-up enough to be readable and understandable for HS students

4. Benefits of an AP CS case study • example of a largish program • opportunity to discuss tradeoffs (design, performance issues, readability, etc) • example of good coding, design, and documentation practice • approximation of master/apprentice • rich source of assignments • source of non-trivial exam questions

5. Alyce’s Additions • describe the development or modification of a program, not just a finished product • cover design • cover testing

6. Goals for Java MBS • provide benefits described in prev. slides • be similar to C++ MBCS • teachers can pick it up faster • can use it as they learn Java • be different from C++ MBCS • highlight differences in language • highlight differences in curriculum

7. The Story • A CS student, Pat, gets a summer job working for marine biologists. • Hired to enhance an existing program that simulates fish movement in a bounded environment. • Needs to understand existing program • Designs, codes, and tests modifications • Occasionally Pat turns to an experienced programmer, Jamie, for help. • Narrative is Pat’s report of summer job.

8. The Package • Code for the “existing” program • Source for core classes • Jar files for “black box” & GUI classes • Javadoc documentation for most classes • Data Files • Instructions for compiling/running • Narrative (pdf file)

9. The Modules (Chapters) • Experiment with existing program • Guided tour of existing program by Jamie • Add breeding and dying • Add two new kinds of fish (inheritance) • Provide alternative representations (unbounded environment, others)

10. Chapter 1 First Day on the Job • “[The program] was designed to help the marine biologists study fish movement in a bounded environment, such as a lake or a bay.” • Jamie available the next day. • Given instructions for running it and told where to find data files.

11. Chapter 2 Guided Tour • “The biologists think of the environment as a rectangular grid, with fish moving from cell to cell in the grid. Each cell contains zero or one fish.”

12. Chapter 2 What classes are necessary? • To model fish swimming in a bounded environment, the program has Fish objects and an Environment object. • The purpose of the program is to simulate fish moving in the environment, so the program also has a Simulation object. • There are other useful, but less important "utility classes."

13. Chapter 2 One step in the simulation

14. Chapter 2 What do core classes look like? • Simulation: almost identical to C++ MBCS • Environment: black box; only look at class documentation (think header file!) • Fish: • has color, direction • move method is a little more complicated, has more helper methods

15. Chapter 2 move method • Get next location to move to (call nextLocation) • If next location is different from this location, • move there (call changeLocation) • change direction (call changeDirection)

16. Chapter 2 nextLocation method • Get list of empty neighboring locations (call emptyNeighbors) • Remove location behind fish from list • If there are any empty neighbors left, randomly choose one; otherwise return current location

17. Chapter 3 Breeding and Dying • Problem Specification: A fish should ... • have a 1 in 7 chance of breeding, • breed into all empty neighboring locations, • attempt to move when it does not breed, • never move backwards, and • have a 1 in 5 chance of dying after it has bred or moved.

18. Chapter 3 Breeding and Dying Pseudo-code for act method if this is the 1 in 7 chance of breeding call the breed method else call the move method if this is the 1 in 5 chance of dying call the die method

19. Chapter 3 Breeding and Dying • Test Plan • Testing random behavior (Chap 2) • Black-box testing • Code-based testing

20. Chapter 4 Specialized Fish • Different patterns of movement • Darters (DarterFish) • Slow fish (SlowFish) • Inheritance • Dynamic Binding

21. Chapter 4 Specialized Fish • DarterFish • darts two cells forward if possible • or darts one cell forward • or reverses direction (without moving)

22. Chapter 4 Specialized Fish • SlowFish • has only a 1 in 5 chance of moving out of current cell • otherwise movement is the same as Fish

23. Classes for A Exam • Class Implementations • Simulation • Fish (as modified in Chapter 3) • DarterFish • SlowFish • Class Documentation • A number of utility classes

24. Chapter 5 Environment Implementations • Multiple environment implementations • Environment Interface • Bounded: 2D array (matrix) -- existing • Unbounded: ArrayList of Fish -- Pat develops this implementation

25. Chapter 5 Environment Implementations • Exercises • Very large bounded environment (list or sparse matrix) • Sorted list for unbounded environment with binary search • BST for unbounded environment • Hash map for unbounded environment

26. Classes for AB Exam • Classes and documentation from A Exam • Additional Class Interfaces/Implementations • Environment • BoundedEnv • UnboundedEnv • Class Documentation • One new utility class

27. Key Features • Overall design & core classes are similar • Discussion of modification/development allows focus on design and testing • Highlights new/different language features • Highlights new topics in curriculum • Inheritance, dynamic binding • Interfaces

28. Want to use it? • www.collegeboard.com/ap/students/ compsci/download.html