FAQ.md

Common issues & FAQ

General notes

1. We only support Java 11. If you use Java 8/9/10, you may encounter unexpected issues and we cannot help you with them. If you've previously installed Java 8/9/10, we recommend that you _ uninstall Java 8/9/10 and install only Java 11_. Read Uninstalling Java if you need a hint on where to start.
2. For debugging, use System.out.println(...) liberally. Make sure to make it easily spottable, e.g. ">>>>>> roundNum" + round, otherwise it might get lost in maven's long output.
3. For JUnit, a test Failure is not the same as Error. If a test fails due to some unexpected exception, then it's an error that has nothing to do with the actual test.
4. Please read the course descriptions carefully. Most of the details you need are there, you just need to take the time to find them and understand them.

Common issues

• During test/runtime:RuntimeException: Implement me
  This is placeholder for you to implement some code. You need to remove the throw new RuntimeException("Implement me"); statement.
• On Windows, 'javac' is not recognized as an internal or external command, operable program or batch file.
  The PATH environment variable is not set up to contain your java installation. Follow the instructions in Setup on Windows.
• javac:cannot find symbol...
  Compilation error, probably syntax related. Or possibly the correct JAVA_HOME environment variable is not set, see the next entry for more details.
• mvnw:Error: JAVA_HOME is not defined correctly; We cannot execute ….
  The export JAVA_HOME=… step is only meant for MVB2.11 Linux lab machines only. Run unset JAVA_HOME to undo this.
• ./mvnw:/bin/bash^M: bad interpreter…
  The mvnw script is broken due to Windows line endings. On Linux, do sed -i -e 's/\r$//' mvnw to fix mwnv. macOS users can try dos2unix.
• mvnw:The goal you specified requires a project to execute but there is no POM in this directory
  The mvnw command should be executed from the project root (where pom.xml is located).
• mvnw:java.lang.UnsupportedClassVersionError:... Unsupported major.minor version 5...
  Maven wrapper needs Java 8 to work, check that the correct JAVA_HOME is set. If this happens on a Mac, make sure that JAVA_HOME is not pointing to the system-bundled Java 6.
• mvnw: Compilation is failing because of warning messages being treated as errors.
  Ideally, you should deal with the warnings so that they don't come up any more. Read the Maven page for more info.
• mvnw: [WARNING] bootstrap class path not set in conjunction with -source 1.8
  You are using the wrong version of Java -- you need to use Java 11! Read the Setup page for instructions on how to uninstall the wrong versions and install the correct one.

FAQ

Q: How do I know what caused a test to fail? What is a stacktrace?
A: A stacktrace tells you which method threw an exception and the path (call trace) that leads up to the exception. Most tests will print some sort of stacktrace in Maven's output (NOTE: adding the -e flag only prints stacktrace for maven internals, not the actual test). If you are still unsure, this tutorial may be helpful.

Q: Can I have multiple returns in a method?
A: Yes, early returns will "short-circuit" and finish the method execution.

Q: I have nested while/for loops and I want to break out of them, what should I do?
A: Refactor the nested loop into a separate method so that you can return early.

Q: Can I use labels in while/for loops?
A: Yes but it is not encourage nor required for any of the coursework.

Q: How does <test method> work?
A: Read the test's method name, and then quickly skim the code (it should read like English). If you are still not sure, consult one of the TAs or ask on the forum.

Q: Why can't I find the implementation for <some interface>?
A: Not all interfaces have implementations, read lecture slides.

Q: Why is the source nested so deep? for example:src\test\java\uk\ac\bris\cs\scotlandyard\...
A: That's how Java packages work, live with it.

Q: Can I use lambdas/streams/functional things/external library?
A: Yes.

Q: Why is <some method> undocumented?
A: Not everything requires documentation (do report this as it could be an oversight).

Q: Can I modify the tests?
A: No.

Q: Can I modify any other files in the coursework?
A: Yes, but it is your responsibility to make sure tests still pass (without modifying them) and the project still compiles.

Q: Do I have to use git?
A: No, you may use any version control software you see fit.

Q: How do I initialise/commit/push/pull/merge/revert/... using git?
A: The Atlassian git tutorials explain most common operations. A quick Google search, e.g. git how to <operation>, should also return plenty of useful resources.

Q: I am getting an error that I haven't seen before. What do I do?
A: Read the error message carefully. It will most likely tell you what's happening and give a hint about where the error originated. Start by investigating there and seeing if you can spot any issues.

Q: I am seeing an error message that I don't understand. What should I do?
A: Use your favourite search engine to search for the error message as it comes up. Using "double quotes" around your search term will make sure the search engine treats it as one single term rather than splitting it up into words. If you get many results, try narrowing things down by adding some keywords related to your problem, e.g. mac/ubuntu/windows, git/java/vim, or eclipse/intellij/atom.

Q: I have not found any help online and I don't think anyone has encountered this problem before. What else can I do?
A: Try a few variations on your search engine query, such as rephrasing your issue or pasting a different part of the error message. If you still cannot find any help, post on the forum, giving a detailed description of the problem and showing the steps to reproduce your issue.

Q: Can I use functional programming concepts (i.e map, flatMap, etc) in the coursework?
A:So the course is called Object Oriented Programming so naturally we want students to learn about OOP and not functional programming. That said, functional programming in Java 8 and above mostly simplifies imperative bits of your program and doesn't reduce OOP as the task has a clear interface that you have to implement. Think of it this way:

By specification, you have to call the makeMove method of the current player with a view of the model. Successfully implementing this requires you to understand that the model is an instance that implements the view interface and that your model interacts with multiple instances of the player type by calling methods(sending messages). If you can explain that clearly then you have achieved the learning outcome. Tasks such as finding the current player or signalling multiple spectator of some events could be done either declaratively through FP or imperatively by iterating through a collection of players/spectators. Because in Java everything is an object (excluding primitives), whatever you pick here, you are technically doing OOP so if you understand how the FP code you wrote works in terms of OOP, I don't see why you shouldn't use it. If you do use FP, be prepared to justify why it is better than the other approaches in your case; the ability to do so will also land you some credits.