CSCI 2600 — Principles of Software
Homework 7: Model-View-Controller
RPI Campus Paths
Due: Wednesday, Aug. 14, 2024, 11:59:59 pm
Submission Instructions
ˆ This assignment uses the same repository as Homework assignments 4, 5, and 6, so when
you are ready to start working on Homework 7, pull Homework 7 ffles from the repository by
right-clicking on your Homework 4 project in Eclipse and selecting Team → Pull... Make
sure that When pulling is set to Merge, then click Finish.
ˆ Be sure to commit and push the ffles to Submitty. Follow the directions in the version control
handout for adding and committing ffles.
ˆ Be sure to include any additional ffles in your repo using Team → Add to Index.
ˆ Important: You must press the Grade My Repository button, or your answers will not
be graded.
IMPORTANT NOTES:
You should have package hw7 with the usual directory structure. Write your code under src/main/java/hw7
and your tests under src/test/java/hw7 (shows as hw7 under src/test/java in Package Explorer).
 If your directory structure is incorrect autograding will fail resulting in a grade of 0!
Introduction
You will be building a route-ffnding tool. It will take the names or ids of two buildings on the
RPI Troy Campus, and generate directions for the shortest route between them, using your graph
ADT to represent buildings and pathways between them. For now you will provide a simple text
interface. In this homework, you will write a complete application runnable from the command
line via a main() method. You will have to name your main class CampusPaths.java for testing on
Submitty.
In this assignment, you will practice modular design, writing code for reuse, and design patterns.
As before, you get to choose what classes to write and what data and methods each should have.
Speciffcally, you will practice the model-view-controller (MVC) design pattern.
For organization, this assignment contains one “problem” for each logical component you will write.
The order of the problems is not meant to suggest an order of implementation. Carefully design
the whole system before attempting to implement any part. Design with “low coupling” and the
“open/closed principle” in mind: you should be able to extend your system, while at the same time
the heart of your system (your model) remains insulated from the changes. As always, you shoulddevelop incrementally, which may mean repeatedly writing a bit of all the parts and verifying that
they work together.
Model-View-Controller
You will design your application according to the MVC design pattern described below. MVC is a
variation of the Observer design pattern discussed in class.
As you design and implement your solution, please list which parts of your code belong to the
model, the view, the controller, or none of the above in answers/hw7 mvc.pdf. Often this can be
on a per-class level, but when a class implements both the view and controller, you must indicate
which methods or lines logically represent the view and which represent the controller. Be sure to
list ALL classes you write for Homework 7. This just should be a list of classes; you don’t need to
write any sentences of explanation.
The Three Pieces: Model, View, Controller
ˆ The model consists of the classes that represent data, as well as the classes that load, store,
look up, or operate on data. These classes know nothing about what information is displayed
to the user and how it is formatted. Rather, the model exposes observer methods the view
can call to get the information it needs.
In general, functionality of a model includes:
– Reading data from the data source (text ffle, database, etc.) to an in-memory representation.
–
Storing data while the program is running.
– Providing methods for the view to access data.
– Performing computations or operations involving the data and returning the result.
– Updating the in-memory state (if the application allows the user to modify data).
– Writing to the data source (text ffle, database, etc.)
ˆ The view implements the user interface. It should store as little data and perform as little
computation as possible; instead, it should rely on the model for data storage and manipulation.
 The view decides how the user sees and interacts with these data.
Does the user interact with a text interface or a GUI? What does the user type and/or click to
get directions from one building to another? How are those directions formatted for display?
What message does the user see upon requesting directions to an unknown building? These
are questions the view answers.
ˆ The controller listens to user input. Based on the user’s keystrokes, mouse clicks, etc.,
the controller determines their intentions and dispatches to the appropriate methods in the
model or view. For a simple interface like in this assignment, the view and controller may besomewhat intermingled in code. Don’t worry too much about the separation there; the key
point for now is that the model is cleanly separated and reusable.
Model-View Interaction
In general, avoid the temptation to create an oversized “god” class that does everything for the
model. The model may contain multiple classes, and the view can interact with multiple classes
in the model. Most of the time, any class that exists solely to represent data is part of the model.
For this assignment, you will likely choose to have one central model class that manages the graph
and does most of the heavy lifting, but you may also want some smaller objects that encapsulate
related data. Some of these objects might be returned to the view so it can access their data
directly, avoiding the “god” class scenario; others might only be used internally within the model.
Your model should be completely independent of the view (UI), which means it shouldn’t know or
decide how data is displayed. The model does know something about what data and operations
the application needs, and it should provide methods to access them; however, it shouldn’t return
strings tailored to a particular view and deffnitely shouldn’t contain printlns. Imagine replacing
your text UI with a GUI or a Spanish/Mandarin/Klingon text UI (but with the same English
building names) and ask yourself: is my model reusable with this new view?
On the ffip side, the view doesn’t know anything about how the model stores data internally.
Someone writing a view for your application should only know that the model somehow stores
buildings and paths on campus and should only interact with the data at this level. In other words,
the public interface of the model should give no indication that these data are represented internally
as a graph. That level of detail is irrelevant to the view, and revealing it publicly means the model
can no longer change its implementation without potentially breaking view code.
Problem 1: Parsing the Data
We have added two .csv data ffles to the data/ directory to be parsed by your application:
RPI map data Nodes.csv and RPI map data Edges.csv. The .csv ffles are comma-separated value
ffles that can be opened in any text editor, just like courses.csv. Their format is described in
more detail below.
As usual, your program should look for ffles using fflenames in your data/ directory e.g.,
data/RPI map data Edges.csv.
You will write a parser to load the data from these ffles into memory. You may use ProfessorParser.java
as a general example of how to read and parse a ffle, keeping in mind that the new data ffles are
structured differently from the RPI Courses data ffle.
The ffle RPI map data Nodes.csv lists all buildings on campus along with their pixel coordinates
on the campus map. The image of the campus map can be downloaded here or a larger version
from here. File RPI map data Nodes.csv has two parts. The ffrst part lists all the buildings on
campus, where each line has four comma separated ffelds:
Name,id,x-coordinate,y-coordinatewhere Name is the full name of the building, id is the building id, and x-coordinate and y-coordinate
are the coordinates on the map. There may be spaces in the building names.
The second part of ffle RPI map data Nodes.csv shows the intersections on the map. The intersections
 have no name, hence the name ffeld is empty.
The ffle RPI map data Edges.csv lists pairs of building and intersection ids:
id1,id2
which means that there is a pathway between the building or intersection denoted by id1 and the
one denoted by id2. Pathways are bi-directional: id1,id2 means that there is a path from id1 to id2
and also from id2 to id1.
Your task is to parse these two ffles and build a graph that represents the RPI campus map. For
this assignment, you will compute the length of a pathway from the coordinates of the end points
by applying the Euclidean distance formula. We will be using the convention that is common in
television and computer graphics where the origin (the point with coordinates (0, 0)) is at the top
left corner of the campus map and the positive Y-axis goes in the downward direction as shown in
the picture below:Another way of thinking about it is imagining that your campus map is in quadrant 4 of your
coordinate plane instead of quadrant 1. In particular, this means that if you ffnd any common
math formulas involving trigonometric functions you might have to adjust them to the coordinate
system used in this assignment by inverting the signs of y-axis parameters. Otherwise, you might
get your computations wrong.
Problem 2: The Model
As described above, the model handles the data and contains the major logic and computation
of your program. For this assignment, a key function of the model will be ffnding the shortest
route between two building on campus. This can be accomplished by using Dijkstra’s algorithm
to ffnd a shortest path in the graph, where edge weights represent the pathway length. Reuse the
Dijkstra method by calling your Homework 6 code. Do not copy and paste your Dijkstra code
from Homework 6 into this homework. Do not re-implement the Graph class in your Homework 7
code. Reuse the Graph class from Homework 4. Do not call methods of GraphWrapper from your
Homework 7 code, use your Graph class directly. If you make changes to code from a previous
homework, be aware that the code must still compile.
Problem 3: The Controller and View
In this homework, you will write a simple text interface. When the program is launched through the
main() method, it repeatedly prompts the user for one of the following one-character commands:
ˆ b lists all buildings (only buildings) in the form name,id in lexicographic (alphabetical) order
of name.
ˆ r prompts the user for the ids or names of two buildings (only buildings!) and prints directions
for the shortest route between them.
ˆ q quits the program. Note: this command should simply cause the main() method to return.
Calling System.exit() to terminate the program will break the tests.
ˆ m prints a menu of all commands. Feel free to add functionality. Our tests cover only the
functionality speciffed above.
When an unknown command is received the program prints the line:
Unknown option
Route directions start with:
Path from Name 1 to Name 2 :
where Name 1 and Name 2 are the full names of the two buildings speciffed by the user. Route
directions are then printed with one line per pathway. Each line is indented with a single tab (

)
and reads:
Walk direction to (Name 3)where direction is the direction of the pathway and Name 3 is the name of the building at the
pathway destination. If the pathway destination is an intersection, print:
Walk direction to (Intersection id)
Direction should be one of: North, NorthEast, East, SouthEast, South, SouthWest, West, or
NorthWest. To determine the direction, compute the angle of the destination from direction north
clockwise (e.g, angle of 90 degrees is East). This angle falls into one of eight 45 degree circle sectors
corresponding to North, NorthEast, East, etc. as shown in the following diagram:
For example, if the angle is in the sector [22.5, 67.5), the direction is NorthEast.
Finally, print the total distance in pixel units:
Total distance: x pixel units.
where x is the sum of the (non-rounded) distances of the individual route pathways.
The total distance should be rounded to three digits after the decimal point. As in Homework 6,
we recommend the use of format strings.
Finally, if one of the two buildings in a route is not in the dataset, the program prints the line:
Unknown building: [Name]
If neither building is in the dataset, the program prints the line twice, once for the first building
and then for the second one. If there is no route between two buildings, your program should print:
There is no path from Name 1 to Name 2.
To help you with formatting your output correctly, we provide several sample files described
in the table below. These files reflect the exact appearance of the console window after running
the program, and include both user input and program output. If you run your program with
the user input shown in the table, the state of the console should match sample file contents
exactly (including whitespace). The sample files and the descriptions above, taken together, should
completely specify the output format of your program.Description Command(s) entered by
the user Sample file
A list of all buildings. b
q
sample hw7 output 00.txt
A path between two buildings.
Buildings are given by their
ids.
r
67
76
q
sample hw7 output 01.txt
A path between two buildings.
Buildings are given by their
names.
r
EMPAC
Academy Hall
q
sample hw7 output 02.txt
No path between two buildings.
Buildings are given by
their names/ids.
r
LINAC Facility
60
q
sample hw7 output 03.txt
One of the buildings is not
found.
r
60
cbis
q
sample hw7 output 04.txt
Both buildings are not found.
r
Louis Rubin Memorial
Approach
102
q
sample hw7 output 05.txt
A path from the building to
itself.
r
East Campus Athletic
Village Arena
89
q
sample hw7 output 06.txt
The menu of all commands.
For this command, your output
may be different from
what is shown in the sample
output file.
m
q
sample hw7 output 07.txt
An unknown command. a
q
sample hw7 output 08.txtSeveral commands in one session.
Problem 4: Testing Your Solution
Unlike in previous assignments, the specification is based solely on the output of the complete
application, as invoked through the main() method. This means that your JUnit tests will be
different from previous homework assignments.
We provide class CampusPathsTest.java as the starter code. The runTest() method takes as a
parameter the name of the test file and then constructs three file names, one for input, one for
expected output, and one for actual output. It temporarily points System.in to the input file and
System.out to the actual output file while it runs your main program. The result is that commands
are read from the input file and output is printed to the output file. For your tests to run, you
simply need to add @Test methods that call runTest() with the appropriate argument. Also, you
might have to edit the designated line in runTest() to invoke your main() method.
You will specify the commands for your tests to run in *.test files. These files simply contain the
input a user would have entered at the command line as the program was running. For each test,
a corresponding .expected file should contain the output your program is expected to print if a
user entered that input. Use JUnit to run the tests. runTest() compares the output in your .out
file against the corresponding .expected file.
Reminder: if a test fails, it is often helpful to look at the .out file. These files are written to the
data/ directory. It might be easier to navigate through the file system using your system’s file
browser or the terminal, rather than in Eclipse.
We have provided one example test in data. Note that the .expected file only contains newlines
printed by the program using System.out.println().It is important that your test data, i.e., *.test and *.expected files, are placed in directory data/
and not in directory src/test/java/hw7/. If you place your test data under test/ Submitty won’t
grab the files and will produce FileNotFound Exceptions.
Additionally, you should write JUnit tests for every class that is not part of the view or controller.
You may not need to write tests for the view and controller. One reason is that they should have very
little functionality — they act as glue between the UI (which is hard to test programmatically) and
the model. Furthermore, end-to-end behavior of your application is tested through the specification
tests. You may write additional tests for your view and controller if you feel there are important
cases not covered by your specification tests, but avoid creating unnecessary work for yourself by
duplicating tests. You must have at least three different path tests. The code instruction/statement
coverage threshold will be set at 85% for this assignment.
Reflection [0.5 points]
Please answer the following questions in a file named hw7 reflection.pdf in your answers/ directory.
Answer briefly, but in enough detail to help you improve your own practice via introspection
and to enable the course staff to improve Principles of Software in the future.
(1) In retrospect, what could you have done better to reduce the time you spent solving this
assignment?
(2) What could the Principles of Software staff have done better to improve your learning experience
in this assignment?
(3) What do you know now that you wish you had known before beginning the assignment?
We will be awarding up to 1 extra credit point (at the discretion of the grader) for particularly
insightful, constructive, and helpful reflection statements.
Collaboration[0.5 points]
Please answer the following questions in a file named hw7 collaboration.pdf in your answers/
directory.
The standard integrity policy applies to this assignment.
State whether you collaborated with other students. If you did collaborate with other students,
state their names and a brief description of how you collaborated.Grade Breakdown
ˆ Quality of test suite, percent of your tests passed: 5 pts. (auto-graded)
ˆ Quality of test suite, percent coverage: 5 pts. (auto-graded)
ˆ Instructor tests: 16 pts. (auto-graded)
ˆ Answers to MVC questions (answers/hw7 mvc.pdf): 5 pts.
ˆ Test data quality (data/*.test and data/*.expected): 3 pts.
ˆ Code quality (src/main/java/hw7/*.java, Principles of Software specs, implementation of
Observer/MVC and code reuse): 15 pts.
ˆ Collaboration and reflection: 1 pt., up to 1 extra credit point (at the discretion of the grader)
for particularly insightful, constructive, and helpful reflection statements.
Hints
Best Coding Practices
When designing classes, keep the single responsibility principle in mind. Avoid huge “god”
classes.
Remember to practice good procedural decomposition: each method should be short and
represent a single logical operation or common task. In particular, it can be tempting to
implement your entire view and controller as one long method, but strive to keep each
method short by factoring operations into small helper methods.
Store your data in appropriate types/classes. In particular, you should not pack together
data into a String and then later parse the String to extract the components.
Remember that your graph should be completely hidden within the model. Classes that
depend on the model (namely, the view and controller) should have no idea that the data is
stored in a graph, not even from the class documentation. If you decided later to switch to a
different graph ADT or to do away with the graph altogether (for example, by making calls
to the Google Maps API to find paths), you want to be able to change the model without
affecting the view and controller, whose job has nothing to do with how the data is stored
or computed.
As usual, include an abstraction function, representation invariant, and checkRep() in all
classes that represent an ADT. If a class does not represent an ADT, place a comment
that explicitly says so where the AF and RI would normally go. For example, classes that
contain only class methods and are never instantiated usually do not represent an ADT.
You very well may find that you have more non-ADT classes on this assignment than in the
past. Please come to office hours if you feel unsure about what counts as an ADT and what
doesn’t.Common Issues
Do not call System.exit() to terminate your program, as it will prevent your specification
tests from passing.
If you use Scanner to read user input from System.in, be sure not to call both next() and
nextLine() on the same Scanner object, as the Scanner may misbehave. In particular,
some students have found that it causes their programs to work correctly at the console but
not when they run their tests. Using Scanner is neither necessary, nor required.
Floating-point precision and numeric comparisons. If you do arithmetic over floating-point
values (float, double), then an exact == may not work as expected. Thus, when comparing
computed floating-point values, you should use an approximate comparison, such as that the
ratio between the values is very close to 1. However, in this assignment you may use == if you
are comparing exact floating-point values that are read from a file, without doing arithmetic
over them. Doing an approximate comparison is even wrong, since it would give someone
reading the code the impression that you are computing approximate values.
What to Turn In
You should commit and push the following files to Submitty. Don’t forget to click Grade My
Repository button on Submitty!
ˆ src/main/java/hw7/*.java
ˆ data/*.test
ˆ data/*.expected
ˆ src/test/java/hw7/*Test.java [JUnit test classes you edit or create]
ˆ answers/hw7 mvc.pdf
ˆ answers/hw7 reflection.pdf
ˆ answers/hw7 collaboration.pdf
Errata
Check the Submitty Discussion Forum for possible errata or other relevant information.
Q & A
None yet.
Parts of this homework were copied from the University of Washington Software Design and
Implementation class by Michael Ernst.
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