AP

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AP Marine Biology SimulationCase Study

• Alyce Brady
• Kalamazoo College

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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

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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

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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 relationship
• context for covering design and testing
• rich source of assignments
• source of non-trivial exam questions

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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

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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 Pats report of summer job.

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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)

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The Modules (Chapters)

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

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First Day on the Job
Chapter 1

• The program was designed to help the marine
  biologists study fish movement in a bounded
  environment, such as a lake or a bay.
• Jamie not available until the next day.
• Pat is given instructions for running the program
  and told where to find data files.

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Exercise 1

• Lets see it run!
• Complete the table on p. 11.

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Guided Tour
Chapter 2

• 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.

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What classes are necessary?
Chapter 2

• 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."

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One step in the simulation
Chapter 2
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What do core classes look like?
Chapter 2

• Simulation step method - very simple loop
  through all the fish (see p. 21)
• Environment black box only look at class
  documentation (until Chap 5)
• Fish
• has color, direction
• move method is a little more complicated, has
  more helper methods

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Constructors
Chapter 2

• Initialize instance variables
• Add the fish to the environment
• a fish knows about its environment
• must always be in an environment to be in a
  consistent state
• See pp. 27-28

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move method
Chapter 2

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

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nextLocation method
Chapter 2

• 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

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Exercise 2

• Lets see some sample exercises.
• Do Questions 1, 7, 8, 9 on p. 31
• Read over exercises on p. 32
• Whats the difference between Analysis Questions
  and Exercises?

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Breeding and Dying
Chapter 3

• 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.

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Breeding and Dying
Chapter 3

• 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

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Breeding and Dying
Chapter 3

• Test Plan
• Testing random behavior (Chap 2)
• Black-box testing
• Code-based testing

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Breeding and Dying
Chapter 3

• 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?

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Exercise 3

• Lets see it run!

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Specialized Fish
Chapter 4

• Different patterns of movement
• Darters (DarterFish)
• Slow fish (SlowFish)
• Inheritance
• Dynamic Binding

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Specialized Fish
Chapter 4

• DarterFish
• darts two cells forward if possible
• or darts one cell forward
• or reverses direction (without moving)

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Specialized Fish
Chapter 4

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

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Exercise 4

• Lets see it run!
• Lets see some sample exercises.
• Questions 1 and 2 on p. 75
• Read over exercises on p. 76

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A Exam Summary

• Class Implementations
• Simulation (Chap 2)
• Fish (Chaps 2 3)
• DarterFish (Chap 4)
• SlowFish (Chap 4)
• Class Documentation
• A number of utility classes

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Environment Implementations
Chapter 5

• Multiple environment implementations
• Environment Interface
• Bounded 2D array (matrix) -- existing
• Unbounded ArrayList of Fish -- Pat develops this
  implementation

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Environment Implementations
Chapter 5

• 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

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AB Exam Summary

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

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Exercise 5

• Lets see it run!
• Lets see some sample exercises.
• Questions 1 and 2 on p. 80
• Read over exercises on p. 104

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Key Features

• Introduces large program to intro students
• Covers key topics highlights new ones
• Object interaction
• Inheritance, dynamic binding
• Interfaces
• Design issues
• Testing
• Data Representation

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Want to use it?

• www.collegeboard.com/ap/students/
• compsci/download.html