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HW3: Mazes Part 1 [PAIR]

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HW3: Mazes Part 1 [PAIR]
This assignment will be due on Wednesday, January 17 at 1 PM and is worth 20
points. You should start early so you have time to ask questions as they come up.
Goal
This assignment will give you some practice designing and writing Java classes and
methods and reading in data from files. It will also prepare you for a future assignment in
which we will use a stack data structure to solve a maze. (In this assignment, we will just
be focusing on printing the maze to the screen.)
This will be a partner assignment. You should work with the partners that I assigned to
you in class.
Reading a maze
You’ll write a class called Maze which will represent a single maze. Maze.java will also
include a main() method that tests the loading and printing of mazes. When you run java
Maze maze.txt, your program should load the maze from maze.txt and print the humanreadable maze to System.out.
For example, if maze.txt looks like:
6 5
0 0
5 4
L-_|_-
|L–|_
|-_-|_
|L|L||
L__L__
then the output should be:
+—–+—–+—–+—–+—–+—–+
| | |
| S | |
| | |
+—–+ +—–+ +—–+ +
| | | |
| | | |
| | | |
+ +—–+ + + +—–+
| | |
| | |
| | |
+ + +—–+ + +—–+
| | | | | | |
| | | | | | |
| | | | | | |
+ +—–+ +—–+ + +
| | |
| | F |
| | |
+—–+—–+—–+—–+—–+—–+
The maze file format
Mazes for this assignment will all be rectangular with walls along the entire outside of the
maze, with no gaps along the outer walls. Rather than an entrance and an exit, there will
be a “start square” and a “finish square”–the goal of the maze solver will be to get from S
to F.
The maze files will have the following structure:
<0-based column number of the start square <0-based row number of the start
square
<0-based column number of the finish square <0-based row number of the
finish square

Each row description includes a single character for each square in that row, and each
character describes the left and bottom walls for its square. (Note: Think about this for a
second. Why do we only need to specify the left and bottom?) Specifically:
• L (uppercase “L”) means that the square has both a left and a bottom wall
• | (vertical bar) means that the square has a left wall, but no bottom wall
• _ (underscore) means that the square has a bottom wall, but no left wall
• – (hyphen) means that the square has neither a left nor a bottom wall.
For example, consider the following (with comments in brackets added that
would not appear in the file itself)
3 2 [The maze has 3 columns and 2 rows]
0 0 [The start square is at the upper left]
2 0 [The finish square is at the upper right]
L-| [(0,0) has left and bottom walls; (1,0) has neither left nor bottom;
(2,0) has just left]
L__ [(0,1) has left and bottom walls; (1,1) has just bottom; (2,1) has
just bottom]
This would yield this maze:
+—–+—–+—–+
| | |
| S | F |
| | |
+—–+ + +
| |
| |
| |
+—–+—–+—–+
Code structure
You will be submitting two files: Maze.java and MazeSquare.java. Skeleton code for these
two files is attached below. The MazeSquare class will contain data about each individual
square in the maze, including which walls it has, whether or not it is a start or end point,
etc. The Maze class will contain an ArrayList of all the MazeSquare objects, and will
contain the functionality for loading and printing the maze.
ArrayLists
The Maze has an instance variable of a type that we have alluded to, but haven’t yet used:
an ArrayList. ArrayLists in Java are similar to the list type in Python. Rather than having
a pre-defined size, like arrays, ArrayLists can have objects added to them and removed
from them dynamically. For example:
ArrayList names = new ArrayList();
names.add(“Sally”);
names.add(“George”);
names.add(1, “Sue”);
for (int i = 0; i < names.size(); i++) {
System.out.println(names.get(i));
}
will print out:
Sally
Sue
George
Some things to notice about this code:
• We had to specify the type of object that the ArrayList contains (in this
case, String). This is done between < and .
• The add() method can be provided one parameter (in which case it adds the given
object to the end of the ArrayList) or two parameters (in which case it adds the
given object to the given index of the ArrayList).
• We cannot use standard indexing notation (e.g., names[i]) to retrieve objects from
an ArrayList, and instead have to use the get() method.
• Other methods may be slightly different, as well. (For example, we used .size() to
get the number of elements in the list, rather than .length.)
We will talk about ArrayLists, and how they are implemented, in great depth next week. For
now, however, you should be able to use them without knowing their implementation. (This
is the power of ADTs!) It will likely be helpful to refer to the Javadoc for ArrayLists and/or
Section 2.2 of the textbook (which is assigned for Monday’s reading).
Getting input from the command line
The Maze class also contains code in its main method for retrieving input from the
command-line. You saw this in CommandLine.java in HW1, which may be worth referring
back to. Arguments to the command-line are stored in the args array as Strings. So, for
example:
public class Test {
public static void main(String[] args) {
System.out.println(String.format(“You said %s”, args[0]));
}
}
would create the following output if run like so:
$ javac Test.java
$ java Test potato
You said potato
If you have questions about the command line (or anything else with the assignment!), feel
free to ask me or your peers over Slack or in person or in email!
Reading Files
As part of the load() method of the Maze class, you will need to read in the contents of a
text file line by line. You can do this using a Scanner class as you have seen before–the
main difference is that we will be passing in a File object instead of System.in. The
skeleton code provided should be enough to get you started (though as always, it may be
helpful to refer to the Javadocs–or the beginning of Section A.10 of the textbook).
Particularly relevant methods to look at are the nextLine() and hasNextLine() methods
from the Scanner class, as well as the split() method from the String class.
Submission and Grading
You and your partner will submit one zip file to just one of your Moodle accounts. This file
should contain MazeSquare.java and Maze.java, fully implemented and commented, with
both of your names in the Javadoc comments. The zip file should be
titled [yourLastName][partnerLastName]HW3.zip (so if I submitted a file with Ethan, it
would be titled AlexanderCasselMaceHW3.zip.
This assignment is worth 20 points. Some of the things we will be grading you on include:
• Does the program compile? It is essential that you check whether your submitted
work compiles. If you submit a program that doesn’t compile, you will automatically
receive at least a 25% deduction for the assignment, even if the problem was
relatively minor.
• Does the program correctly take maze files as input through the command-line?
• Does the program print mazes correctly? There are two maze files included here,
which should be good test cases, but you should create your own test cases, as
well! Think about how different kinds of mazes might throw off your printing
functionality.
• Are both of your files well documented, including Javadoc-style comments for each
class and method, as well as in-line comments to describe the logic behind
individual tasks you perform within methods?
• Do your variable and method names make sense?
• Do you make good decisions as to what is public vs. private, and whether variables
are instance variables or local to the methods in which they are used?
As always, start early, and have fun!

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