In the previous assignment, UW Marketing commissioned you to write a route finder tool. Marketing is pleased with your initial results, but now they've asked for a graphical user interface (GUI) that visually draws routes on a map.

You will build your GUI using Java's Swing and Abstract Windowing Toolkit (AWT) libraries. You will get practice using Swing, event-driven programming, and the model-view-controller (MVC) design pattern.

When you're done, you can share your finished work with family and friends by following the instructions for creating a JAR file.

You are expected to fix any bugs from Homework 8 that affect the correctness or performance of your application in Homework 9. However, you are not required to fix code quality/organization issues in your Homework 8 code. Your Homework 9 code should be well-written and well-organized, but we will not double-count for MVC-related style issues caused by design choices from Homework 8.

Checker Framework Required Changes

Please follow the required checker framework steps as done in homework 7 by adding the @SuppressWarnings("nullness") annotations to any .java files you create. Please remember to run ant validate on attu to make sure you have done this on all necessary files.

GUI Requirements

You will write a GUI and a main class to launch it named This assignment is deliberately open-ended: the exact appearance and functionality of your GUI are up to you. The only requirements are documented below.

For the most part, we are not grading on aesthetics: it doesn't matter whether your GUI looks pretty as long as it implements the required features. Nevertheless, a design that is genuinely confusing or hard to use (at our discretion) will not receive full credit. For example, we will deduct points if we can't easily figure out how to select the two buildings, if it's hard to see the selected path, or if we can only see the whole GUI on your 27-inch monitor. In addition, your program should be generally responsive: for instance, the GUI should not take an unusually long time to find and display paths.

Your GUI is a new View and Controller for your CampusPaths application. Ideally, you should not have to make any changes to your Homework 8 model classes — they already implement all the Model functionality that you need. If you have to make any small changes (for instance, if your design in Homework 8 was poor and some model methods were too closely tied to your text view), then you may do so. As always, all tests from previous homeworks must continue to pass, so you may also need to change your Homework 8 View and Controller in that case. In file hw9/answers.txt, list any changes you made to the model. For each, write a 1-2 sentence explanation of why the change was necessary and what you could have done differently on Homework 8 to create a more general and reusable Model. If you make no changes this file should just contain “None”.

Window size

At startup, your GUI must fit and be usable on a screen with a minimum of 1024 x 768 resolution. (You may wish to support resizing the window, but doing so is not required.) Most computers provide a way to change the screen resolution, which you can use for testing.

Required features

At a minimum, your GUI must provide the following features:

Swing widgets and GUI builders

Use only components from the Swing widget set for this assignment. You are also allowed to use components from AWT, on which Swing is built, but try to stick to Swing when possible.

Some IDEs, such as NetBeans, will let you specify the appearance and behavior of your GUI and automatically generate the code for you. You may not use these tools; you must write your GUI from scratch in Java.

Launching your GUI

Because you probably didn't write automated unit tests for your GUI, ant won't be useful for this assignment. Instead, you can manually launch your GUI from the command line by running the following commands:

  cd [PathToYourCse331Project]/cse331/src/hw9
  ant build
  cd ../..
  java -cp bin hw9.CampusPathsMain

Those are the commands we will run when grading your program.

If you log into attu via ssh, but when you try to run your GUI on attu you get a message similar to

Exception in thread "AWT-EventQueue-0" java.awt.HeadlessException:
No X11 DISPLAY variable was set, but this program performed an operation which requires it.

then you need to enable X11 forwarding for your ssh session. If you are are using Linux, this can be done using the -Y switch when starting ssh:

ssh -Y

If you normally use Windows, the most straightforward option is simply to log onto one of the Linux workstations in the basement labs to test your program (from these machines use ssh -X to connect to attu. Alternatively, you can obtain special software to enable X11 forwarding on Windows. One free option is Xming used with PuTTY. After installing Xming, launch PuTTY, select "Enable X11 forwarding" under Connection >> SSH >> X11, and log in as normal. Please note that the course staff many not be able to provide complete support for enabling X11 on Windows.


Writing automated tests for GUIs is important, but it is difficult and usually involves special frameworks that are beyond the scope of this course. For this reason, you are not required to write unit tests or a test driver. We will test your solution by running your main program.

Optional Extra Features

We encourage you to get creative with both the appearance and functionality of your GUI! If you do, make sure to get a basic GUI working and commit it to your repository before experimenting. Swing can be finicky, and seemingly simple UI improvements often become big time sinks. If you've committed your working solution, you can always “roll back” to that revision later.

Here are a few ideas for additional features:

List any additional features you implemented, if any, in hw9/answers.txt. Additional features must not mask or replace any of the required features.

Small amounts of extra credit may be awarded for interesting or useful functionality that shows considerable effort. Please make sure the you have the required features functioning before working on the extra credit, and that any extra features you implement do not override or change the required features. Extra credit will not be awarded for pure “eye candy,” such as changing the font and color of buttons or adding a border. Extra credit will be applied to final course grades after determining initial course grades; thus, it will not lower your grade if you choose not to work on optional features, but may raise your grade slightly if you do.

Checker Framework EXTRA CREDIT

Another way to earn extra credit is through the checker framework again. For up to 5 extra credit points remove as many of the @SuppressWarnings("nullness") as you can and try to add the nullness annotations in your code. Not that you can also add the @SuppressWarnings("nullness") directly above individual methods instead of above the whole class.

No matter how much work you do for the extra-credit, please really make sure you run ant validate on your final submission to verify your work builds and your tests pass. Because if ant validate fails because of the nullness checker than the build will fail when our grading scripts run, and you will not pass any of the tests. It is important that the rest of your work for this homework assignment is counted correctly.

Please use the provided resources to help you with this. You can review the checker framework lecture. You can also see the checker framework manual.

Because this is extra-credit, the TAs will not provide help in regards to checker framework annotations in Piazza or through Office Hours. You can definitely use Piazza to discuss ideas regarding annotations amongst each other, but please refrain from posting large, revealing sections of your code that display work done for other parts of this assignment.


General GUI Advice

If you've never used Swing, it is well worth your time to do some tutorials, read the example code, and generally get comfortable with GUI programming before diving into the assignment. Take it from your peers: in the past, many students who choose the latter approach have reported to us afterward that they wish they had chosen the former.

Abstraction functions, representation invariants, and checkRep() are not required for GUI classes because they generally do not represent ADTs.

User testing is a great way to verify that your interface is as easy to use as you think it is. Show your GUI to your friend/roommate/sibling. Can they can figure out how to use it without directions from you?

As usual, remember to practice good procedural decomposition among other best practices for style. In particular, your GUI constructor and paintComponent will probably be long enough that they should be broken into helper methods.

Programming With Swing

In addition to the lecture slides and demos, Oracle's Swing and 2-D Graphics tutorials are a useful resource. Also remember to use the Java API, particularly the javax.swing and java.awt packages, to see what classes and methods are available and how to use them.

To display the map and routes, you will want to write a custom component and override paintComponent(). You will use Graphics and/or Graphics2D to do the rendering, as we saw in lecture.

If you have trouble getting things to display at the correct size, make sure you have remembered to call pack() before setting your frame to be visible.


As usual, your program should look for files using relative filenames starting with src.

What to Turn In

You should add, commit, and push the following files to your GitLab repository:

Additionally, be sure to commit and push any updates you make to your Homework 8 files.

When you have committed and pushed all of your changes and are done with the assignment, you should create a git tag in your repository named hw9-final and push that tag to your repository. Once you have committed and pushed that tag, your assignment has been submitted and the staff will grade the files in your repository that are labeled with that tag.

Finally, remember to run ant validate to verify that you have submitted all files and that your code compiles and runs correctly when compiled with javac on attu (which sometimes behaves differently from the Eclipse compiler).