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COMP122 Assessment 3 Worth 25% of the final course mark. Submission Deadline Friday, 27 April 2018, 5:00pm (Friday of Week 10) Learning Outcomes. This assessment addresses the following learning outcomes of COMP122: • Describe object hierarchy structure and how to design such a hierarchy of related classes. • Describe the concept of object polymorphism in theory and demonstrate this concept in practice. • Identify and describe the task and issues involved in the process of developing interactive products for people, and the techniques used to perform these tasks. Part I (50% of assessment mark) Introduction Note: This problem is inspired by a problem encountered on DataCamp’s “Data Science with Python” career course. (http”//www.datacamp.com) Figure 1: A reference to Franz Kafka’s The Metamorphosis. Illustra- tion by Jir̆ı́ho Slı́vy. Random walks. We have previously encountered the idea of a random walk in this module in the course notes and practical ses- sions. We’re going to explore this concept in this part of the assess- ment. Cockroaches at work (or play?). Consider two cockroaches that are moving up and down the staircase visiting the 102 floors of the Empire State Building (the iconic building in New York City). In case you don’t know, (some) cockroaches can fly, so can sometimes move very quickly. We are going to assume that these cockroaches move (somewhat) at random, and we want to examine some aspects of their movement. In particular, suppose that each cockroach starts on the ground floor of the Empire State Building, which we will label as “floor 1”. During a single timestep of movement, each cockroach could move up or down one or more floors, or could possibly stay stationary. Their movement is governed by a random process, which can be different for each cockroach. (These details are given below for the two cockroaches we will consider here.) The types of questions we are usually interested in when considering random walks include: 1. How long does it take a cockroach to reach the top floor? 2. After walking for a certain number of timesteps, what is the highest floor that has been reached during that period? 1 http://www.datacamp.com 3. How often are the two cockroaches on the same floor during their random walks (assuming they both start in the same place)? 4. How long is it necessary for the cockroach to walk before it is at a “random floor” of the building? (This depends upon trying to more precisely define what we mean by this statement.) Since we’re dealing with random processes, we really want to consider averages for these answers, i.e. if we repeat the process a large number of times (with different random inputs), what is, say, the average maximum height reached during a fix time period? Even the use of the word “average” should really be clarified. Does this word refer to the “mean”, the “mode”, or the “median” (or some other concept)? If you aren’t aware of these different meanings, you should really learn what they are as sometimes the word “average” is used in (say) news reports without really specifying which one is meant, or the word “average” is used in a misleading way. If I were to tell you that the mean salary of employees in a company is £60,000 and the mode of the salaries is £25,000, what might this suggest about the salary of the “average employee” of that company? In any event, the goal of this part of the assignment is to write code to answer these types of questions posed about the random walks of the cockroaches in question. (Don’t worry, I will define what “average” refers to when we get to the questions we want to answer. . . ) Ideally we can use Java’s object-oriented capabilities (and maybe some polymorphism) to help us write our code as we are dealing with cockroaches all the time, but ones with some slightly different behavior in how they move about the Empire State Building. Figure 2: The Empire State Build- ing. Photo by Sam Valadi https://www.flickr.com/photos/132084522@N05/17339180506, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=62752443 Terminology. In what follows, I will use the word “timestep” or simply “step” to refer to one “unit of time”, which is the amount of time necessary for a cockroach to move exactly once. It is possible that during this single move the cockroach could traverse several floors, or possibly remain stationary, but at the beginning of a time step the cockroach is on some floor, and at the end of the timestep it has moved once (or possibly remained stationary) and is again on some floor of the building (i.e. not “in between” floors). The floors of the Empire State Building building are numbered sequentially starting from the “ground floor” (with value 1) to the “top floor” (numbered 102). (Note that while many tall American buildings don’t have a floor numbered “13”, the builders of the Empire State Building weren’t superstitious, so it does have a “13th floor”. Note also that the cock- roaches don’t have access to the secret 103rd floor of the Empire State Building.) A cockroach can never go below the ground floor, nor above the top floor, so if it was to try a move that would take them too low or too high, it can instead move to the ground floor or top floor, but not beyond. (For example, if a cockroach was on floor 101 and was going to move up 3 floors, it would instead move to floor 102 and stop. If it started the timestep on the ground floor and wanted to move down, it would instead remain stationary for that step.) 2 Our subjects. We are going to consider two cockroaches, named Don and Bella. Don likes to show off his big wings and, thus, generally likes to move up more than down, but unfortunately Don is also a bit clumsy. In any single time step, this is how Don moves: (1) With a 0.1% chance, Don flies into the center of the stairwell and ends up falling all the way back to the ground floor. (2) Otherwise, Don rolls his 6-sided die (since we all know cockroaches love to carry around and use dice) and does the following: (a) On a 1 or a 2, Don moves down one floor. (b) On a roll of a 3, 4, or 5, Don moves up one floor. (c) On a roll of a 6, Don re-rolls his six-sided die and moves up the number of floors equal to this second roll of the die. Figure 3: An artist’s rendition of Don (or maybe Bella, I for- get. . . ). Our other cockroach, Bella, has wings that are just as big as Don’s and she also generally likes to move up rather than down, but Bella is lazy and doesn’t usually move as fast as Don. Fortunately for Bella, she isn’t clumsy like Don, but she does like to stop at the observation deck on the 86th floor to enjoy the view. Bella moves as follows: (1) If Bella is pausing for a view on the 86th floor, she doesn’t move at all for one step, and in the next step will roll her die (after all, she is a cockroach too!) to (possibly) move. (2) Otherwise, Bella rolls her 6-sided die and does the following: (a) On a 1, 2, or 3, she moves down one floor. (b) On a 4, she moves up 2 floors. (c) On a 5, she moves up 3 floors. (d) On a roll of a 6, Bella doesn’t move. (e) However, if Bella moves onto (or tries to move through) the 86th floor, she will stop on floor 86, and will pause for a view on the next step. (So if, for example, Bella was on floor 85 and rolled a 4, she would stop on floor 86 for a view on the next step, instead of progressing to floor 87.) If Bella rolled a 6, and was already on floor 86, she will still pause for a view on the next step. (Note that this means Bella will spend two time steps on floor 86, one for the step when she rolled a 6, and another when she pauses for the view, as described in (1) above.) Remember that neither Don nor Bella can ever go below the ground floor (floor 1) nor above the top floor (floor 102), so if they try to do that, they will move as far as they are able and then stop. Requirements Your goal is to implement Java classes to represent the cockroaches, so that we can gather some emprical knowledge about the random walks in the Empire State Building. You should note the following: (1) (Requirement) Develop an abstract class called “Cockroach.java”. This class should have an abstract method called takeStep() (taking no parameters), which will be implemented by subclasses. This method defines what a cockroach does in a single timestep of movement. The Cockroach class should have an attribute for a name of the cockroach (a String), and can have other class attributes, con- stants, and methods as you deem appropriate. You can, for example have an attribute that keeps track of the number of steps the cockroach has taken since it started its random walk. You will, of course, need an attribute that keeps track of its current location (floor) in the Empire State Building, which the takeStep() method should update. 3 Be sure to include appropriate “get” or “set” methods as you need them and/or other methods you want to include in the Cockroach class. (2) (Requirement) Each individual cockroach should be a subclass of “Cockroach.java”. Only include additional attributes in the subclasses as you need them (i.e. in good object-oriented programming style, put as many of the attributes, methods, and constants into the base “Cockroach.java” class as you can). Obviously each subclass will need to implement the takeStep() method above which determines how the cockroach moves in a single timestep of its movement. As mentioned, you can include additional atributes, constants, or methods beyond those in “Cockroach.java”, but these should be integeral to a particular cockroach and not ones that could be included in that base class. (3) (Requirement) You are going to output some summary statistics that you gather after repeating some experiments. DO NOT USE an external library to compute these statistics! Write some (short) methods to compute these numbers as appropriate. Make certain the values that you output are double values. Do the following experiments: (a) For each of our two cockroaches, starting from the ground floor, have them each walk for 100 timesteps. (By “walk” I mean execute their takeStep() method.) Record the maximum floor that each cockroach reaches during the course of their walk.