AP Marine Biology Simulation Case Study Alyce Brady

AP® Marine Biology Simulation Case Study Alyce Brady Kalamazoo College

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

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

Benefits of an AP CS case study n n n n 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 relationship context for covering design and testing rich source of assignments source of non-trivial exam questions

Goals for Java MBS provide benefits described in prev. slides n be similar to C++ MBCS uteachers can pick it up faster ucan use it as they learn Java n be different from C++ MBCS uhighlight differences in language uhighlight differences in curriculum n

The Story n n 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. u Needs to understand existing program u Designs, codes, and tests modifications Occasionally Pat turns to an experienced programmer, Jamie, for help. Narrative is Pat’s report of summer job.

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

The Modules (Chapters) Experiment with existing program (run it) n Guided tour of the code by Jamie n Add breeding and dying n Add two new kinds of fish (inheritance) n n Provide alternative representations (unbounded environment, others)

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. ” n Jamie not available until the next day. n Pat is given instructions for running the program and told where to find data files. n

Exercise 1 n Let’s see it run! n Complete the table on p. 11.

Chapter 2 Guided Tour n “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. ”

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

Chapter 2 One step in the simulation

Chapter 2 What do core classes look like? Simulation: step method - very simple loop through all the fish (see p. 21) n Environment: black box; only look at class documentation (until Chap 5) n Fish: uhas color, direction umove method is a little more complicated, has more helper methods n

Chapter 2 Constructors Initialize instance variables n Add the fish to the environment ua fish knows about its environment umust always be in an environment to be in a consistent state n See pp. 27 -28 n

Chapter 2 move method Get next location to move to (call next. Location) n If next location is different from this location, umove there (call change. Location) uchange direction (call change. Direction) n

Chapter 2 next. Location method Get list of empty neighboring locations (call empty. Neighbors) n Remove location behind fish from list n If there any empty neighbors left, randomly choose one; otherwise return current location n

Exercise 2 n Let’s see some sample exercises. u. Do Questions 1, 7, 8, 9 on p. 31 u. Read over exercises on p. 32 n What’s the difference between Analysis Questions and Exercises?

Chapter 3 Breeding and Dying n Problem Specification: A fish should. . . uhave a 1 in 7 chance of breeding, ubreed into all empty neighboring locations, uattempt to move when it does not breed, unever move backwards, and uhave a 1 in 5 chance of dying after it has bred or moved.

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

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

Chapter 3 Breeding and Dying n Sample Exercise: Introduce a new instance variable in Fish keeping track of how many times a fish bred. Initialize it in the constructor and increment it in the breed method. Modify the debugging statement in the die method to print the number of times the fish bred. Run your simulation for 20 timesteps. What is the maximum number of times a fish bred in your test run? What is the minimum number? Are these values you would have expected given the probability of breeding in each timestep?

Exercise 3 n Let’s see it run!

Chapter 4 Specialized Fish Different patterns of movement u. Darters (Darter. Fish) u. Slow fish (Slow. Fish) n Inheritance n Dynamic Binding n

Chapter 4 Specialized Fish n Darter. Fish udarts two cells forward if possible uor darts one cell forward uor reverses direction (without moving)

Chapter 4 Specialized Fish n Slow. Fish uhas only a 1 in 5 chance of moving out of current cell uotherwise movement is the same as Fish

Exercise 4 n Let’s see it run! n Let’s see some sample exercises. u. Questions 1 and 2 on p. 75 u. Read over exercises on p. 76

“A” Exam Summary Class Implementations u. Simulation (Chap 2) u. Fish (Chaps 2 & 3) u. Darter. Fish (Chap 4) u. Slow. Fish (Chap 4) n Class Documentation u. A number of utility classes n

Chapter 5 Environment Implementations n Multiple environment implementations u. Environment Interface u. Bounded: 2 D array (matrix) -- existing u. Unbounded: Array. List of Fish -- Pat develops this implementation

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

“AB” Exam Summary Classes and documentation from “A” Exam n Additional Class Interfaces/Implementations u. Environment u. Bounded. Env u. Unbounded. Env n Class Documentation u. One new utility class n

Exercise 5 n Let’s see it run! n Let’s see some sample exercises. u. Questions 1 and 2 on p. 80 u. Read over exercises on p. 104

Key Features Introduces “large” program to intro students n Covers key topics; highlights new ones u. Object interaction u. Inheritance, dynamic binding u. Interfaces u. Design issues u. Testing u. Data Representation n

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