In part 1 of this assignment, you will design a graph ADT and write tests for it. (You will not implement the ADT until part 2.) You get to specify the ADT (choose its operations), and write tests to demonstrate that an implementation meets the specification.

Although this is an individual assignment, in the design stage you will learn more and produce a better design by bouncing your ideas off others and incorporating their own ideas. To encourage discussion, we are relaxing the standard collaboration policy somewhat for Part 2 (the interface design stage). You must first attempt to come up with an interface design on your own, but then you are strongly encouraged to discuss your design with your classmates who have also attempted a design (as well as the course staff during office hours) as much as you like, without restrictions on what materials you can bring to or from meetings. On the other parts of this assignment, the standard collaboration policy still applies.

This assignment is the first of a multi-part project. Think about building a campus map to get an idea of one application for your graph ADT. By the end of the quarter, you will build a full application for getting directions to travel between two buildings on the UW campus. Remember that the goal here is to design a resusable ADT - specializing your graph for the "map" application would only weaken the reusability of your code.

This assignment assumes that you have read and understood the handout about abstraction functions and representation invariants. If you have not read it, do so now.

You will reuse and extend the graph ADT in future assignments. Do the best you can, but you should expect to improve your design and refactor your implementation over the course of the quarter.

Part 1: Written Exercises

This part is designed to test your understanding of some of the ADT concepts from lecture. To get started, update your working copy of your repository by pulling from git to get the files for this assignment. Create a PDF file with your answers to these questions and submit it to Gradescope.

  1. For each of the classes below, write the abstraction function and representation invariant, referring to the source code provided in the graph/problem1 package of your project.

    1. IntQueue1
    2. IntQueue2
  2. Below are several snapshots of an IntQueue2 object's internal state at different points in a program. Which snapshots are equivalent to each other at the abstract level? In other words, partition the snapshots into groups based on which are identical to each other from the client's perspective.

    Diagrams of a queue in various states
  3. Below are signatures for various methods and constructors. For each, state and justify in 1-2 sentences (per part) whether the method or constructor could possibly expose the representation, given the information available. Explain any assumptions you made.

    1. public int solveEquations(int x, int y, int z)
    2. public String[] decode(boolean slowly)
    3. private Date myBirthday()
    4. public String toString()
    5. public Iterator<Integer> elements()
    6. public Deck(List<Card> cards)

Graph Definitions and Terminology

In the rest of this assignment you will design a directed labeled graph and write tests for it, but you will not implement it. (You will lose a very significant amount of points if you implement it.)

A graph is a collection of nodes (also called vertices) and edges. Each edge connects two nodes. In a directed graph, edges are one-way: an edge e = ⟨A,B⟩ indicates B that is directly reachable from A. To indicate that B is directly reachable from A and A from B, a directed graph would have edges ⟨A,B⟩ and ⟨B,A⟩.

The children of node B are the nodes to which there is an edge from B. In Fig. 1, the children of B are A and C. Similarly, the parents of B are the nodes from which there is an edge to B. In Fig. 1, B has only one parent, A.

A path is a sequence of edges ⟨node1,node2⟩, ⟨node2,node3⟩, ⟨node3,node4⟩, .... In other words, a path is an ordered list of edges, where an edge to some node is immediately followed by an edge from that node. In Fig. 1, one possible path is ⟨B,A⟩,⟨A,B⟩,⟨B,C⟩. This path represents traveling from B to A to B to C. A path may traverse a particular edge any number of times.

In this class, your graphs can have any number of edges (zero, one, or more) between a pair of nodes (this kind of graph is often known as a multigraph). Fig. 2 shows a graph with 2 edges from A to C.

In a labeled graph (Fig. 3), every edge has a label containing information of some sort. Labels are not unique: multiple edges may have the same label. For this project, you may assume that no 2 edges with the same parent and child nodes will have the same edge label. (Whether or not you do make the assumption, make sure it is clearly documented so clients understand how they can use your ADT.)

A simple directed graph
Figure 1: A simple directed graph with four nodes.
A graph
Figure 2: A directed graph.
A labeled graph
Figure 3: A directed labeled graph.

If you want to learn more, read Wikipedia's definition of a graph. If you still have questions, ask the course staff.

Many interesting problems can be represented with graphs. For example:

Part 2: Write a Specification for Graph

To start, you will specify the API for a Java class or classes representing a directed labeled graph. The API, or public interface, is the collection of public classes and methods that clients of your graph ADT can use. We recommend that you work in iterative layers of detail. Start rough — preferably with pencil and paper — by identifying what operations the ADT needs to support, how it might be logically broken into classes and interfaces, and how these classes and interfaces rely on each other. Then, jot down a list of methods for each class that provide these operations. Think through some possible client applications, particularly the application in UW campus map, to get an idea for what operations are needed. Perhaps write some pseudocode (or even real code) for the application and make sure your graph interface meets its needs. (Note: don't worry about implementing the search algorithm - in fact, you should not add a sorting algorithm. We prefer that you focus on the lower-level operations needed to build the graph and to be able to perform some search. We'll be looking at how to search a graph in later assignments.)

Keep your initial design rough — don't write formal class and method specifications with all the proper clauses right away. Your design will likely go through multiple iterations, and it's easier to throw away parts if you have invested less effort in them.

You may find the Test Script File Format section to be helpful in determining, at minimum, the functionality your graph must be able to satisfy. Implementing the test script commands as a client of your graph should be a trivial matter.

Once you are satisfied with your high-level design, write a Javadoc specification for each class and method. Follow the CSE 331 format, remembering to use both standard Javadoc tags (param, return, throws) and ones introduced for this course (spec.requires, spec.effects, spec.modifies). A good approach is to create skeleton implementations of your classes containing only method “stubs” for public methods, then write your specifications in the right place in the source file. A stub is a not-yet-implemented method whose body simply throws an exception, as you saw in the polynomial assignment starter code. Stub methods give you the flexibility to compile client code and tests before all your methods are implemented correctly.

As you write the Javadoc specifications and create the stub methods, review the HTML API documentation produced by the javadoc tool. You can invoke the javadoc took by running the "javadoc" task under the "documentation" category for your gradle project. Reviewing specifications in this format can provide useful feedback on the quality and completeness of the work you've done. After you run the javadoc tool, you can view the generated docs by right clicking on the file hw-graph/build/docs/javadoc/index.html and choosing "Open in Browser."

You may assume nodes are uniquely identified by their data contents: that is, no two nodes store entirely equal data.

For this assignment, you should restrict your graph to store the data in nodes and edge labels as Strings. We strongly recommend you DO NOT use Java generics for this assignment. Students who have had an informal introduction to Java generics, and who try to use generics on this assignment, tend to struggle on subsequent assignments. CSE 331 will give a more disciplined introduction to generics. After that, you will use generics to make your ADT work with other data types — text, integers, doubles, etc.

Because you are defining a single abstraction (a graph), you should generally define a single top-level class. (You may choose to define a top-level interface as well.) It is OK to use helper classes, but they should be inner classes — much like Map.Entry is a nested interface of Map. Note that inner classes can be public and used by clients, as Map.Entry is. (If the inner class is an implementation detail, it should be private. If it is a publicized part of the ADT specification, it should be public.) You can create other top-level classes that are not part of the graph implementation, if necessary.

Why should there be only one top-level graph class? It would be bad style to spread a single abstraction across multiple public top-level classes. Using multiple public top-level classes leads to an implementation and a rep invariant that is distributed across multiple classes rather than being local as it should be. Putting your abstraction in a single top-level class makes it easier to understand and verify. In some cases (though not for public helper classes!), helper classes are implementation details, so their existence exposes the representation — a client could come to depend on them, restricting your ability to change the implementation in the future.

Implementation details, such as fields, representation invariants, and abstraction functions, and private inner classes, are not part of the public specification. Therefore, they should not be part of what you submit for this assignment.

Design problems such as this one are open-ended by nature: we are not looking for one “right” design. There are principles of good design you have learned in lecture, however. You will also find suggestions of what to consider and how to approach the problem in the hints section. Also, designs naturally evolve as requirements change, so try to make your code easy to expand without making it overly general right away. You are allowed to change the design in the future, and most students do, as they discover limitations of their original design or invent better designs.

In your PDF file from Part 1, write a brief description of why you included the operations you did and why you feel they are a sufficient interface to a graph. If your design includes multiple classes or interfaces, explain why you included each one; if not, explain whether you considered additional classes and why you decided not to include them. So your total work in this part is this brief write-up plus the Javadoc class and method specifications as they appear in the source code; you do not need to submit the Javadoc comments in a separate file, nor the generated API documentation (.html files). You should, however, make sure that the javadoc tool works without error before you turn in this assignment - we'll be using the javadoc tool to read your specifications when grading this assignment. The gradle javadoc task can help you find and fix any formatting or documentation errors you might have.

Part 3: Write Tests for Graph

Write a high-quality test suite for your Graph specifications. It's important to write your tests before your code. You'll be writing tests for your graph in two different ways:

  1. Script Tests: Because we didn't specify any of the class or method names you need to write for this assignment, we cannot test your interface directly. Instead, you will construct script test cases in the format specified in the Test Script File Format section. Each test case should consist of a “test” file containing a series of commands, and an “expected” file containing the output that the commands should produce. The file names should have the same base name but end with .test and .expected, respectively. For example, you may have a command file named testAdd.test with expected output in testAdd.expected. These files must be in the hw-graph/src/test/resources/testScripts/ directory. They should have descriptive file names and comments that explain what case is being tested, and just like methods in unit tests, each test file should test only one distinct condition. It is okay to include many operations in a single test, but those operations must be focused on testing one particular behavior. Think of each .test/.expected pair as the equivalent to one method in a JUnit test suite - you'll probably have a large number of them. The staff supplied GraphTestDriver will read from these files using the format described and "run the tests". For now, you don't have to implement the driver.
  2. JUnit Tests: For any behavior that you weren't able to fully test using the script tests, you should write unit tests in one or more JUnit test classes, just like you saw in the setup and polynomial homework assignments. In general, you want to create one test class per public ADT class. Since you wrote stubs in your class(es), you should write tests that call and test the stubs as if they were implemented. Therefore, once you implement the stubs in the next assignment, you should be able to run your JUnit tests without having to edit those files. You should put junit tests you write in hw-graph/src/test/java/graph/junitTests. Note: You'll likely need to import your graph code (import graph.*;) in your JUnit tests in order for the code to compile.

The combination of the script tests and the JUnit tests should be a complete and thorough test suite for your graph. In general, you should try to test as much behavior as possible using the script tests first, then only add any supplementary tests needed as JUnit tests for anything that you can't write using the script testing language. Depending on your design, this may mean that you have very few JUnit tests (if the majority of your program's behavior can be tested using the script language).

Documentation: In the same PDF file from Parts 1 and 2, write a paragraph or two (maximum) documenting and explaining your testing strategy. Mention how your script tests differ from your JUnit tests (if they do) and why.

Note that both your script tests and your JUnit tests will fail, because you have not yet implemented your graph. They should succeed after you implement your graph in the next assignment. Therefore, you don't need to try to run your tests for this assignment. Your code should compile correctly, however. You can use the hw-graph:validatePart1 gradle task, under "hw-graph > Tasks > homework" in the gradle menu, to verify that your code compiles and the javadocs generate successfully.

It is important to check every aspect of the output files to make sure that your tests are running correctly, including whitespace. We use an automated script to compare the expected and actual output of your files and report if they don't match.

Test Script File Format

Because you and your classmates will have different specifications for the class(es) in this assignment, it is important that there is a standardized interface to use and test your code. To that end, we specify a text-based scripting format used to write instructions that will be executed by your graph.

The testing script is a simple text file with one command listed per line. Each line consists of words separated by white space. The first word on each line is a command name. The remaining words are arguments to that command. To simplify parsing the file, graph names and node and edge data may contain only alphanumeric ASCII characters (in other words, numbers and English letters (upper or lower case)).

Each test that you write will consist of two files with the same name, but one with the .test extension, and the other with the .expected extension. When the tests are run, the test driver will read each line in the .test file and execute the corresponding command (or simply echo it, as described below) then add the output of that command to a file that it generates with the same name but an .actual extension. After the test is complete, the .actual file looks exactly like the .test file but every command has been replaced with the output of running that command. To determine if the test has passed, the test driver compares the contents of the .expected and .actual files. If they match exactly, the test passes. If there's some difference between what was "expected" and what "actual"lly happened, the test fails.

Remember - in part 1 of this assignment you haven't implemented graph yet, so your tests are expected to fail and you don't need to try to run them. For reference for future assignments, the .actual files will generate in hw-graph/build/resources/test/testScripts/. It can sometimes be helpful to look at the contents of the .actual file to see what went wrong when debugging in later assignments. IntelliJ can help with this - select both the .expected and .actual files for a test in the IntelliJ file browser, then right click on one and choose "Compare Files". In the testing window at the bottom of IntelliJ after running tests, IntelliJ will also often provide a "Click to Show Difference" link when you have a failed test selected, which uses the same tool.

The following is a description of the valid commands. Each command has an associated output that's generated when the command is executed. Lines that have a hash (#) as their first character are considered comment lines and are only echoed to the output when running the test script. Lines that are blank should cause a blank line to be printed to the output. These commands were chosen for ease of testing and are not meant to suggest what methods you should include in your graph specifications or how you should implement them. For example, it is unlikely to make sense for your graph ADT to store a name for the graph.

CreateGraph graphName

Creates a new graph named graphName. The graph is initially empty (has no nodes and no edges). The command's output is:

created graph graphName

If the graph already exists, the output of this command is not defined. Note that graph names are used purely in the test script - they allow you to create a use multiple graphs within the same test; it is unlikely to make sense for your graph ADT to store a name.

AddNode graphName nodeData

Adds a node represented by the string nodeData to the graph named graphName . The command's output is:

added node nodeData to graphName

If a node with this data is already in the graph, the output of this command is not defined.

AddEdge graphName parentNode childNode edgeLabel

Creates an edge from parentNode to childNode with label edgeLabel in the graph named graphName. The command's output is:

added edge edgeLabel from parentNode to childNode in graphName

If either node does not exist in the graph, the output of this command is not defined. If an identical edge (same parent, child, and label) already exists, the output of this command is not defined either, as it is left to your discretion whether to allow identical edges in your implementation.

ListNodes graphName

This command has no effect on the graph. Its output starts with:

graphName contains:

and is followed, on the same line, by a space-separated list of the node data contained in each node of the graph. The nodes should appear in alphabetical order. There is a single space between the colon and the first node name, but no space if there are no nodes.

ListChildren graphName parentNode

This command has no effect on the graph. Its output starts with:

the children of parentNode in graphName are: 

and is followed, on the same line, by a space-separated list of entries of the form node(edgeLabel), where node is a node in graphName to which there is an edge from parentNode and edgeLabel is the label on that edge. If there are multiple edges between two nodes, there should be a separate node(edgeLabel) entry for each edge. The nodes should appear in lexicographical (alphabetical) order by node name and secondarily by edge label, e.g. firstNode(someEdge) secondNode(edgeA) secondNode(edgeB) secondNode(edgeC) thirdNode(anotherEdge). There is a single space between the colon and the first node name, but no space if there are no children.

Sample input and output

We have provided example input and output files in your hw-graph/src/test/resources/testScripts/ directory. You may assume the input files are well-formed.


Writing Specifications

To give you some sense of the kinds of issues you should be considering in your design, here are some questions worth considering. These don't in general have simple answers. You'll need to exercise judgment, and think carefully about how different decisions may interfere with each other.

In choosing what operations/methods to include, strive to include enough that the ADT will be convenient and useful for a client, but avoid the temptation to write an “everything but the kitchen sink” API. Generally speaking, it is better to design a minimal than a maximal API. In the real world, you can always add methods later. However, you can never remove them from a published API, and such methods may over-constrain the implementation in the future.

Make good use of the course staff. If you have concrete questions, then take your specification to office hours for feedback on your design and style. Doing so could save you a lot of time.

Designing Tests

It can be difficult to come up with a good test suite. You would like to test a variety of “interesting” graphs, but what are interesting graphs? One possible approach is a “0, 1, 2” case analysis: test scripts with 0, 1, and 2 graphs are interesting; graphs with 0, 1, and 2 nodes and 0, 1, and 2 edges are interesting. For each method, 0, 1, and 2 parameters and 0, 1, and 2 results are interesting; for example: AddEdge on nodes that currently have 0, 1, and 2 children; ListChildren on nodes with 0, 1, and 2 children; etc. This approach, while certainly not required, can give a good way to structure your tests to cover many important cases without too much redundancy. Following only this approach doesn't guarantee that you've written a good test suite, though, so make sure you apply the knowledge you've gained in lecture and section and ask questions if you're confused.

You also may want to think about specific kinds of Graphs, and test those cases separately. For example: what might go wrong if your graph has a cycle in it? What if there are "islands" - multiple different groups of nodes that have no edges connecting them? What about other "odd" Graphs?

IntelliJ and .test files

IntelliJ may prompt you to install a plugin for .test files. Don't install it, IntelliJ is misunderstanding what we're using the .test files for. Just manipulate .test files as text.

How to Turn In Your Homework

Refer to the Assignment Submission Handout and closely follow the steps listed to submit your assignment. Do not forget to double check your submission as described in that handout - you are responsible for any issues if your code does not run when we try to grade it.

Use the tag name hw5-part1-final for this assignment. Note: The regular gradle validate task attempts to run the tests for an assignment. Since your tests are expected to fail for this assignment, you should use the the grade task: hw-graph:validatePart1 to verify your code on attu.

Your TA should be able to find the following in the your repository:

Don't forget to submit your written answers to Gradescope, in addition to submitting the code through GitLab.

Q & A

Q: Does the graph ADT have to support an edge connecting a node to itself?

A: Yes. It's common for graphs to have these kind of nodes, so your ADT should allow them.

Q: Does the graph ADT have to support multiple edges between the same nodes with the same text?

A: No, you can choose if you'd like to support this as part of your design.