CS 455 Programming Assignment 1
Fall 2021 [Bono]
Due date: Wednesday, Sep. 15, 11:59pm Pacific Time
Introduction
In this assignment you will write a graphics-based program to simulate someone tossing a
pair of coins some number of times, and display the results. So for example the user may
request 10 trials. For each trial two coins are tossed. The program reports in bar graph form
how many times the result was two heads, how many times it was two tails, and how many
times it was one of each.
This assignment will give you practice with creating and implementing classes, using loops,
using the java library for random number generation, doing console-based IO, drawing to
a graphics window, and writing a unit test. Also you'll get practice in general program
development. Please read over the whole assignment before beginning: in particular, do
not wait until the assignment is due to read about submitting it because you'll want to do
your first submit before the final deadline, because when you submit it we do some checks
on your code, and you will be able to resubmit if you fail those checks (but not if you are
out of time).
This document may seem voluminous, because it includes some instructional material, and
hints on how to do certain things. You'll need to read it or parts thereof more than once,
possibly skimming some parts on the first reading. To help you find things as you are
working on the assignment, here is a table of contents for the main sections:
Table of Contents
Resources
The programming environment for this assignment
The assignment files
The assignment
More details of the error-checking
Class design
Incremental development
Testing the CoinTossSimulator class
Hints on graphics programming
How to communicate information between objects
README file
Grading criteria
How to turn in your assignment
Resources
Horstmann, Section 2.9, 2.10, 3.8, How-to 3.2 Programs that draw stuff
Horstmann, Chapter 3, Implementing Classes
Horstmann, Section 4.3.1, Reading input
Horstmann, Section 6.9.1, Random numbers and Simulations
The programming environment for this assignment
Reminder: The first time you access the assignment on Vocareum, you will need to go
through the link on d2l (More detailed directions about this were given on Lab 1). Any
subsequent accesses to the same assignment can be made via labs.vocareum.com.
In the normal Vocareum configuration, you have a Linux terminal, but no way to run a
program with a graphical user interface (GUI). For this assignment we are using a different
Vocareum configuration that will allow you to open multiple windows, including a separate
one to run your GUI program. With this configuration, when you start up Vocareum for this
assignment, it will not start up a terminal in the workbench window (i.e., the usual one you
use), but you use a virtual Linux desktop instead.
How to start up a virtual Linux Desktop in Vocareum
The way you get to a virtual linux desktop in this assignment is to go to a menu that's on
the upper right of the workbench window: choose Actions--> Applications --> Desktop.
That will open a linux desktop in another tab in your browser. If it starts with a pop-up
dialog, choose "Use default configuration." There are a few ways to open a terminal
window in this desktop. You can use the Applications menu at the top left of the screen,
and choose "Terminal Emulator". Or you can right click anywhere on the desktop, and
choose "Open Terminal Here".
Warning: depending on how you started up terminal, it might not start out in your home
directory (i.e., "work"), but rather starts in the root directory ("/") or somewhere else. So the
first thing you should do is
cd
to get into your home directory. (One way to check if you are in your home directory is you
will see the ~ (tilde) right before the $ in the shell prompt.)
Your home directory will be populated with the starter files we are providing you. Part of
what we provided is source code for a complete sample Java GUI program there, so you
can try out compiling and running such a program in this environment before you write
code for your own program. Compile and run this program:
javac CarViewer.java
java CarViewer
More about this car example (from Section 3.8 of the textbook) later.
You can switch between these two tabs in your browser to switch between editing (normal
Vocareum window), and compiling and running (Linux desktop). To make it easier to see
your compile errors at the same time as you view your source code, you can put the
Vocareum tab in a different browser window altogether.
Another option with the desktop is to use one of the other source code editors available
within the desktop itself. I saw emacs and vim (Rt-click on desktop-->Applications--
>Accessories). I'm not sure how fast these work on this platform, so if you end up using
one of these, let me know how it goes. (I only opened emacs there briefly once; it started
up pretty fast, so that's a good sign.) Both emacs and vim are a little different than other
editors you are used to, so you probably would want to take a look at an online tutorial on
the web before using them. Eclipse is also available there; it may be somewhat slower than
running it locally.
You can disconnect from the Desktop by closing the tab, or in the main Vocareum window
(upper right) do: Actions-->Applications-->Stop App. Then you can restart later the same
way you did the first time.
Using another IDE for this assignment
If you don't want to use Vocareum and its Linux desktop as your development
environment, you can use another IDE running locally on your own machine.
If you choose go this other route, you would do the following:
1. Install and try out another IDE. There are a few tutorials in the Java section of the
Documentation page to help you get started with IntelliJ or Eclipse.
2. Download the starter files for the assignment into a folder on your laptop (e.g., call it
pa1). The easiest way to do this is, from the Vocareum PA1 assignment workbench do:
Actions-->Download starter code (menu on the upper right).
3. Get your program working, tested, and completely documented on your laptop IDE,
and when you are ready to turn it in . . .
4. Upload your complete program into Vocareum. In the Vocareum workbench, click
Upload (button in the upper-left area), and you will get a file browser that will allow
you to select multiple files to upload. You will only need the source code files (and
README), no .class or project files. Do not wait until the final due date/time is
imminent before uploading and testing it on Vocareum.
5. Compile and completely test your program again on Vocareum. You want to make
sure what you wrote will run in the Vocareum environment, because it is the grading
environment. This also helps you to make sure that you are going to be submitting
the correct version of your solution.
6. Submit your assignment on Vocareum. Please read the details about submitting this
in the section on it at the end of this document.
The assignment files
The files in bold below are ones you create and/or modify and submit. The ones not in bold
are files you will use, but that you should not modify. The ones with a * to the left are
starter files we provided.
* CarViewer.java, CarComponent.java, and Car.java. The code for the example in Section 3.8
of the textbook. For more about why these are in the starter files, see the section on
class design.
* CoinTossSimulator.java Your CoinTossSimulator class. The public interface is provided.
You will be completing the implementation and a test driver for it.
* Bar.java A Bar class. The public interface is provided. You will be completing the
implementation of it.
CoinSimViewer.java Your CoinSimViewer class. You create this file and class.
CoinSimComponent.java Your CoinSimComponent class. You create this file and class.
CoinTossSimulatorTester.java Your unit test program (a.k.a., test driver) for your
CoinTossSimulator class. You create this file and class.
* CoinSimViewer.list A list of the .java files for compiling the CoinSimViewer program. For
more information about this, see the subsection on compiling multi-file programs.
* README for more about what goes in this file, see the section on README file. Before
you start the assignment please read the following statement which you will be
"signing" in the README:
"I certify that the work submitted for this assignment does not violate
USC's student conduct code. In particular, the work is my own, not a
collaboration, and does not involve code created by other people, with the
exception of the resources explicitly mentioned in the CS 455 Course
Syllabus. And I did not share my solution or parts of it with other students
in the course."
For more information about the classes mentioned above see the section on class design.
The assignment
Initially your program will prompt for the number of trials to simulate (a trial is two coin
tosses) on the console (i.e., terminal window), error checking that a positive value is
entered. (More details about error checking here.) This part of the program will be console-
based, to keep things simpler.
Then it will run the simulation and display a 500 tall by 800 wide pixel window with the
results of that simulation. The results will consist of three labeled bars, each a different
color, to show how many trials had the specified outcome. The label will show what the
outcome was (e.g., Two Heads), the number of trials that had that result, and the
percentage of trials that had that result (rounded to the nearest one percent). Because the
simulation uses random coin tosses (simulated using a random-number generator)
subsequent runs with the same input will produce different results.
Here is a screen-shot of output from one run of our solution to this assignment, where we
do 1000 trials:
Remember, your output will not be identical to this because of the random nature of the
results. As you can see in this example, because of the rounding, depending on the results,
the total of all the percentages might not add up to exactly 100%.
Note the placement of each of the bars evenly across the window. In addition, the height
of each bar is given so that 100% would fill up most of the height of the window (but not
run into the top of it). Thus the 49% of trials that resulted in a head and a tail in the
example above fills up roughly half of the height of the window.
Also, your bar graph should get resized appropriately if the window gets resized. As
mentioned in the textbook, every time a window gets resized or iconified and de-iconified
paintComponent gets called again. Here's a later screen-shot created during same run shown
above, but after the window had been resized:
Note that resizing the window does not change the results of the simulation.
Here's an example illustrating what the display looks like when all of the trials have the
same result, forced here by only doing one trial: Note that the bar does not touch or run
off the top of the screen)
More about the graphics library methods necessary to get these results in the section on
Graphics programming.
There are a few other requirements for the assignment discussed in the following sections.
To summarize here, the other requirements are:
you must create and use the classes mentioned in the section on Class design.
you must create a working unit test program for your CoinTossSimulator class, describe
further in the section on Testing the CoinTossSimulator class.
you must edit and submit the README file discussed in the section about that. Do not
wait until you are about to submit the program to answer the README questions,
because they involve further tests of your program, and you may discover a bug
during that testing.
your program will also be evaluated on style and documentation. More about this in
the section on grading criteria.
More details of the error-checking
As mentioned in the earlier section, when your program prompts for the number of trials,
you will error check that a positive value is entered. More specifically, we mean that on an
invalid number of trials the program will print out an informative error message and then
prompt and read again until the user enters a valid value. Example (user input shown in
italics):
Enter number of trials: -5
ERROR: Number entered must be greater than 0.
Enter number of trials: 0
ERROR: Number entered must be greater than 0.
Enter number of trials: 100
Your program does not have to handle non-numeric input. (We will not test it on that
case.)
Class design
To help you make your program object-oriented, we are giving you the general class
design for this program.
The Car Example
Our program follows the conventions of graphical classes used in the textbook (see
Resources, near the beginning of this document, for relevant textbook readings). In
particular, this general design follows the car example in Section 3.8 of the textbook that
has a viewer, a component, and a graphical object that can get instantiated multiple times
and drawn in different locations on the screen (in that one the object class is a Car, here it's
the Bar).
We provided you with the source code for that example as part of the starter files for this
assignment. You can use the code in CarViewer as a starting point for your CoinSimViewer
class for this assignment.
In addition to examining the general structure of the car example code, you can use it to
test out running a GUI program in the Vocareum virtual Linux Desktop before developing
your own code. When you run it there, you can also see how the display changes when you
change the size of the window in which the CarViewer application is running and the
corresponding code that gets that to happen (the display for your program will also
change when the window is resized).
We also modified CarComponent.java a little bit from the version of the code from the text:
we instrumented the code, so you can easily see every time paintComponent gets called, to
help you better understand when the Java Swing graphics framework calls
paintComponent. To see this, once you start running the program, make sure you can see
the terminal window, as well as the CarComponent window; then try resizing the
CarComponent window, and minimizing it and opening it again.
You are required to use the following classes (ones in bold are ones you will be creating
yourself or implementing):
CoinSimViewer . Contains the main method. Prompts for the number of trials, and creates
the JFrame containing the CoinSimComponent. Besides CoinSimComponent, this class does not
depend on any of the other classes mentioned here (e.g., if one of those other classes
changed, CoinSimViewer would not have to change.) The later section on communicating
information between objects will be useful when developing this and the next class
listed.
CoinSimComponent . Extends JComponent. Constructor initializes any necessary data and
runs the simulation. Overrides paintComponent to draw the bar graph, using Bar objects
for each bar in the graph. This class uses the CoinTossSimulator and Bar class.
CoinTossSimulator . This is the class responsible for doing the simulation. It has no
graphical output, and in fact, does no I/O to the console either. It has a run method to
run a simulation of tossing a pair of coins for some number of trials. It has accessors
to get the results of the simulation. Subsequent calls to run add trials to the current
simulation. To reset the CoinTossSimulator to start a new simulation, call the reset
method. For examples of how it operates, see the sample output of the test program
from the section on testing this class.
We are giving you the exact interface to use for this class. By interface, we mean what
clients need to know about the class to use it, i.e., the class comment, the method
headers and associated method comments. Do not change the interface when you
incorporate it into your own program. For all assignments in this class, when we say
that, we mean no changing the provided method headers, no adding public methods,
no removing public methods. As part of the grading process, we will be using our
own test programs with such classes, and if you change the public interface your code
might not even compile with our test programs.
CoinTossSimulator does not depend on any of the other of your classes or the graphics
library. It does use Random (described further below). The skeleton code for
CoinTossSimulator is in CoinTossSimulator.java.
Bar . For drawing a bar in a bar graph. You specify the location, dimensions and color
of the bar in the constructor. The only other method is draw which draws the bar given.
We are giving you the exact interface for this class. (See the previous bullet point for
more details about what we mean by that.) Bar does not depend on any of the other
of your classes, but does use the graphics library. The skeleton code for Bar is in
Bar.java.
CoinTossSimulatorTester . A program to test your CoinTossSimulator class independently
from its use in the CoinSimViewer program. It will have its own main method. This class is
described in more detail in the section on testing the CoinTossSimulator class.
java.util.Random. The java random number generator. See section 6.9 of the textbook
for examples of its use. One thing to note about Random: it's a class that through a
sequence of method calls generates a sequence of values that depend on the internal
state of the object (in this way it is similar to Scanner). Students often want to create a
new Random object every time they want a new random number. Don't do that. Instead,
normally you create one Random object in your program, and then whenever you want a
new random number you make another call to nextInt on that same object. (If you
create a Random object every time you are not generating a pseudo-random sequence,
although it will appear that you are.)
To reflect what would be going on in the real-world version of these trials, your
program must generate one random number to simulate a single coin toss.
Note: this list doesn't include all the java library classes that will be used in the program; for
example CoinSimComponent will need java.awt.Graphics.
Incremental development
Any program of non-trivial size will be developed faster, with fewer bugs, using the
technique of incremental development, which means developing, and testing, pieces of the
program incrementally. The incremental aspect is that your program may gradually grow
until it includes the complete functionality. (Other people use different names for the same
thing. Sometimes it's called building subsets.)
A desirable feature of individual classes is that they are as independent as possible from a
program that uses them. Some classes, such as String, or ArrayList (which we will see soon)
are general-purpose and can be used in many different programs. Other classes are more
special-purpose, such as CoinTossSimulator, but still are modules that can be separated from
a particular program that uses them. We can test such a module using a unit-test, which is
a program specially designed to test the module.
We often unit-test one (or more) classes, and then once we are convinced that unit is
working correctly, we can integrate that class with other code that uses it. If this larger
code base is now buggy, we can feel fairly certain that the bug is in the new code we
added, since we already tested the first class. So any time we find bugs, it's in a small
program: much easier than locating bugs in large programs.
Similarly, if we make later changes or enhancements to our application our code will be
more robust in the face of these changes because, in our unit-test, we tested the module in
ways not specific to how it was used in this application. (As you have experienced as a user,
software is always getting changed over time, e.g., the latest version of Windows is in the
double-digits.) For example, in this assignment, there are methods and method
functionality of CoinTossSimulator that are not used by the program that draws the bar graph,
but you would never be sure whether they worked if you didn't test them.
For this assignment, the final product will not be a very large program, but we want to get
you in the practice of using incremental development, so you will still be successful when
you are trying to develop and debug much larger programs. Even in this program there are
at least two distinct issues to deal with: (1) figuring out how to use the random-number
generator to do a coin-toss simulation and (2) figuring out how to do the graphics to draw
the results of the simulation. It will be much easier you we can deal with these issues one at
a time, so you can isolate bugs related to each one more easily. For this assignment you
are required to write a console-based Tester class to test your CoinTossSimulator class. This
test program is described in more detail in the next section.
Similarly, you could test your Bar class apart from its use in this particular bar graph by
creating several bars with hard-coded data or data from the keyboard using a Scanner. We
won't require you to submit such a BarTester program for this assignment, however.
Testing the CoinTossSimulator class
You are actually going to submit two programs for this assignment, both of which use your
CoinTossSimulator class. One is CoinSimViewer, described earlier, that has a graphical display.
The other is a console-based program, CoinTossSimulatorTester, expressly written to
thoroughly test your CoinTossSimulator class, without including the drawing functionality of
the CoinSimViewer program. The rationale for unit tests was discussed in the previous section.
First, here's more information about compiling Java code:
How to compile and run multi-file Java programs on the command line Often you can
just list the file that contains main in the compile command and javac figures out what other
classes are used in that program and compiles those as well. However, sometimes the Java
compiler gets confused when you only have modified some of the source files since the
original compile. For running a program that uses multiple class files, the only class name
you give as the argument to the java virtual machine is the one containing main.
When you are compiling and running your test program you should be able to do it as
follows:
javac CoinTossSimulator*.java
java CoinTossSimulatorTester
The wild-card ("*" symbol) in the compile command will match the two files
CoinTossSimulatorTester.java and CoinTossSimulator.java.
For the larger program we are doing for this assignment (for that one main is in
CoinSimViewer.java), you can either list all of the files it uses on the command line or use the
following convenient shorthand:
javac @CoinSimViewer.list
java CoinSimViewer
The CoinSimViewer.list file (one of your starter files) just consists of the list of files to compile
for the program. The @ on the command line tells java to look in the file that follows it find
out what java files to compile. An alternate is to use *.java instead in the compile
command, although that one would also attempt to compile CoinTossSimulatorTester.java as
well as the code for the car example.
As mentioned in the previous section a test program like CoinTossSimulatorTester is called a
unit test; we have discussed such unit tests in lecture, and they are also discussed in
Section 3.4 of the textbook. One goal of this test program is for you to test the full
functionality of the CoinTossSimulator class. However, its use in the CoinSimViewer
program does not test the full functionality. In particular, with the CoinTossSimulator you
can do multiple calls to the run method to add more trials to the ones already made. AND if
you call reset does it reset the simulation back to its beginning state (i.e., no trials done
yet).
So, what should you put in your CoinTossSimulatorTester? This will be a console-based
program -- i.e., no GUI. It will be a non-interactive program (i.e., fixed data, nothing read in
from the user), that tests every method multiple times, printing informative output to the
console with the results of each operation. Make sure you also test creating and using
multiple instances of the class.
Unlike the unit-test programs in the textbook and lecture, we can't predict the exact results
of calls to run, because of the random nature of the program. Instead, write code to test
that the sum of the number of two-head tosses, two-tail tosses, and head-tail tosses adds
up to the total number of trials. (Hint: In the sample output below, we display true or false
for this result by just printing out the result of a boolean expression. So if we ran it on a
buggy CoinTossSimulator, it might result in false. NOTE: we WILL be doing such a test on
your test program.)
Your output should look like the following. This shows only part of a sample run of our
tester program. A few explanatory notes first:
exp below means expected results. These are meant to be computed a different way
than the actual results (i.e., you would not call getNumTrials() for the value).
the part in italics is not the literal output you should produce, but describes what we
left out here. The parts in red are parts we would like you to pay particular attention
to here -- your output will not appear in red.)
After constructor:
Number of trials [exp:0]: 0
Two-head tosses: 0
Two-tail tosses: 0
One-head one-tail tosses: 0
Tosses add up correctly? true
After run(1):
Number of trials [exp:1]: 1
Two-head tosses: 0
Two-tail tosses: 1
One-head one-tail tosses: 0
Tosses add up correctly? true
After run(10):
Number of trials [exp:11]: 11
Number of trials:
Two-head tosses: 2
Two-tail tosses: 3
One-head one-tail tosses: 6
Tosses add up correctly? true
After run(100):
Number of trials [exp:111]: 111
Two-head tosses: 28
Two-tail tosses: 30
One-head one-tail tosses: 53
Tosses add up correctly? true
[ . . . output for tests with different number of trials would be here . . .]
After reset:
Number of trials [exp:0]: 0
Two-head tosses: 0
Two-tail tosses: 0
One-head one-tail tosses: 0
Tosses add up correctly? true
After run(1000):
Number of trials [exp:1000]: 1000
Two-head tosses: 265
Two-tail tosses: 229
One-head one-tail tosses: 506
Tosses add up correctly? true
[ . . . output for other tests would be here . . .]
Remember you won't get these exact numbers because of the random nature of the
simulation.
Note: When you test a method such as run which has a restriction on its parameter (in this
case the restriction is that the value must be greater or equal to one) it means that the
behavior of the method is undefined if that precondition is not met. That means that your
code for run does not have to handle that case, and your tester program should not test
that case.
Hints on graphics programming
Most of the graphics primitives you will need for this program are covered in the graphics
sections at the end of Chapters 2 and 3 of the textbook, except for a few things we will
discuss here. So, you will not need to go hunting through the online documentation or
random web sites to figure out how to do the necessary drawing. More specifically: how to
draw a filled rectangle is illustrated in the alien face example in textbook section 2.10.4;
and the start of the section of this assignment on class design discusses another example
from the textbook that has a similar object-oriented design to this one.
Your program may use a fixed size for the width of each bar, and for the buffer-space
between the tallest possible bar and the top and bottom of the window (the solution
whose results we showed earlier also does this). Any such constants in your program need
to be named constants (see section on grading criteria below, for more information). For
the purposes of this assignment you do not have to worry about the fact that if we resize
the window small enough horizontally, the labels centered under each bar, and eventually
the bars themselves will start running into each other.
(Note: named constants would also be helpful to map the bar colors to what they are used
for, e.g., constant HEAD_TAIL_COLOR.)
The JComponent methods, getWidth() and getHeight(), which get the width and height of the
component, will come in handy here. Since CoinSimComponent is a subclass of JComponent you
can directly call those methods from your component object. For an example of such calls,
see the CarComponent class included in the starter code (and discussed further here).
To make sure all the necessary information appears on the window and in the right place,
you will also need to know the dimensions of the label you will be displaying (here we'll
just use the default font size for the given graphics context). This is not covered in the
textbook, so here is a code snippet:
String label = "Hello, world!"; // suppose this is the label you want to display
Font font = g2.getFont();
FontRenderContext context = g2.getFontRenderContext();
Rectangle2D labelBounds = font.getStringBounds(label, context);
int widthOfLabel = (int) labelBounds.getWidth();
int heightOfLabel = (int) labelBounds.getHeight();
The following diagram illustrates some of the specification for how the window should be
laid out -- it is not meant to show coin-toss output, per se. (You may want to compare this
with the earlier screenshots.) It will also help illustrate the meaning of the parameters to
the Bar constructor.
x bars are evenly spaced: center of middle bar is centered in window. Depends on the
window size.
bw bar width. This is a fixed value in the program.
vb vertical buffer. This is a fixed value in the program. Tallest bar means the tallest
possible bar you could draw (i.e., for this program, if all the trials came out the same
way).
label1, label2, etc. labels on a bar. These are centered under each bar.
s (s is for scale) one application unit in pixels. So, this bar is five application-units high
(applicationHeight is 5) The scale depends on window size.
To relate the last item to our program: scale and applicationHeight are parameters to the Bar
constructor. For our program the application unit in the bar graph is a coin-toss trial.
How to communicate information between objects
There are several techniques to communicate information between classes and methods of
classes, including via parameters and return values of methods. In particular, here you have
the issue of receiving some information in main in CoinSimViewer, that is, the number of trials,
but needing to use that information in the component. To do this, your CoinSimComponent
class will need to have its own constructor (Note: this is different than the simpler
component examples in the book). From main you can pass the information to that
constructor, and then, if you also needed access to it in other methods, you would save it
in an instance variable.
Recall that you never will be calling paintComponent yourself, nor are you allowed to change
the parameters to it.
README file
For this and all other programs you will be required to submit a text file called README with
your assignment. In it you will initial the certification we mentioned earlier. This is also the
place to document known bugs in your program. That means you should describe
thoroughly any test cases that fail for the the program you are submitting. (Not your bug
history -- just info about the version you are submitting.) You should also document here
what subset your solution implements if you weren't able to complete the whole program
(more about that in the next section). You can also use the README to give the grader any
other special information, such as if there is some special way to compile or run your
program (this would be unusual for students who complete the assignment).
For this program, also put the answers to the following questions in the README:
1. In CS 455 what code from the web are you allowed to use in your assignment
solution, assuming you modify that code once you get it? (No clue? Hint: Reread the
syllabus.) Note: no need to mention the "starter files" for the assignment in your
answer.
2. What is the probability of each of the three outcomes in a trial: two heads, one head
and one tail, and two tails? Why is one of them different than the other two?
3. Roughly how many trials do you need to do before you mostly get results within 1%
of these probabilities? Do several simulations using your program to determine an
answer to this.
4. Roughly how many trials can you do before it crashes with an overflow error? State
the largest value you tried where it still worked correctly, and one where it
overflowed. You can get an idea of what general values to try by looking at the limits
on Java integers (see Section 4.1.1 of the text). Play around with your program to
verify that it actually works for very large values that are within the limits. Note: this
kind of testing can sometimes turn up bugs, so it's good to do. Warning: For very
large values you may have to wait a fair amount of time before you get the results.
Grading criteria
This program will be graded based on correctness, style, and testing. Programs that do not
compile will get little or no credit. However, an incomplete program can get some
correctness points if it has partial functionality (you document the partial functionality in
the README, discussed above). This grading policy is to encourage frequent testing of subsets
(discussed earlier in the section on incremental development). Also, for incomplete
programs, the style score will be scaled according to how much is completed.
We have published a more complete set of style guidelines for the course on the
assignments page, but here are a few things to pay particular attention to for this program:
documentation. You need to supply an overall comment for each class, and detailed
comments about the interface of each method (so called method comments). For the
main program you need to supply a comment describing what the program does, and
how to run it: this would go above the main class definition. (We have already
provided the class and method comments for the CoinTossSimulator and Bar classes
since we specified those interfaces for you.) This was described in more detail in
lecture and the textbook (see Section 3.2.4). Use in-line comments where necessary to
explain any confusing code ("this is a for loop" type comments are not helpful).
named constants. There are some numbers mentioned in the assignment description
as well as other values that are described to be "fixed" in the program. Each of these
should be given a descriptive name (e.g., BAR_WIDTH) in the program so it would be easy
to change the value later. Named constants in Java are discussed in section 4.1.2 and
programming tip 4.1 in the textbook.
private data. You should never need public data. Rather, clients should only be able to
access data through methods. The rationale for this is discussed in section 3.1.3 of the
textbook.
good identifier names. Use descriptive names for variables, parameters, and methods.
Also use Java naming conventions. Details in item 8 of course style guidelines.
Sections 2.2.3 and 4.1.2 of the textbook discuss more about naming.
good/consistent indenting. Use the conventions from the textbook or lecture.
For this program only, you do not have to worry too much about method length (guideline
#9), and while you should document any instance variables that are not obvious from their
names, you do not have to worry about representation invariants (item #17).
Implementing the required class design and answering the README questions will also be part
of your style/documentation score.
How to turn in your assignment
Make sure your name, NetID, course, assignment, and semester are at the top of each file
you submit (for source files, they would be inside of comments), for any assignment you
submit for this course. You will lose a point on any assignment for which this information is
missing. Note: your NetID is the part of your USC email address before the @
The files you need to submit are the ones shown in bold in the earlier section on
assignment files.
No matter where/how you developed the code, we will be grading it on Vocareum using
the java compiler and virtual machine there (Version 1.8, aka Java 8).
If you developed your program outside of Vocareum, for example, using Eclipse on your
laptop, you'll need to upload your code to Vocareum and retest it completely before you
submit it. Do not wait until the final due date/time is imminent before testing it on
Vocareum. Please read the earlier section on using another IDE for more details on this.
How to submit your program When you are ready to submit the assignment press the big
"Submit" button in your PA1 Vocareum work area. Do not wait until the final due date/time
is imminent before attempting to submit for the first time. You are allowed to submit as
many times as you like, but we will only grade the last one submitted.
What happens when you click submit. Vocareum will check that you have the correct files
in your work area and whether they compile. Passing these submit checks is not necessary
or sufficient to submit your code (the graders will get a copy of what you submitted either
way). (It would be necessary but not sufficient for getting full credit.) However, if your final
submitted code does not pass all the tests we would expect that you would include some
explanation of that in your README. One situation where it might fail would be if you only
completed a subset of the assignment (and your README should document what subset
you completed.)
The results of the submit checks will appear on your terminal window. You can also access
them by going to the "Details" menu, and choosing "View Submission Report". Please read
this report to see if you passed the tests, so you can fix your program and resubmit if
necessary. Make sure you scroll down to the bottom of the report so you dont miss
anything.
If you are unsure of whether you submitted the right version, there's a way to view the
contents of your last submit in Vocareum after the fact: see the item in the file list on the
left called "Latest Submission".

欢迎咨询51作业君