CS++ Java — Assignment Workflow Guide

Step-by-step instructions for completing and submitting Java assignments

This guide walks you through the complete workflow for every CS++ Java assignment — from accepting the GitHub Classroom link to checking your autograded score.

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Table of Contents

1. Overview
2. Step 1: Accept the Assignment
3. Step 2: Open GitHub Codespaces
4. Step 3: Understand the Project Structure
5. Step 4: Write Your Code
6. Step 5: Run Tests Locally
7. Step 6: Read Test Output
8. Step 7: Commit and Push
9. Step 8: Check Your Autograded Score
10. Practice Without Breaking Tests
11. Common Code Patterns
12. Troubleshooting
13. Tips for Success
14. FAQ

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Overview

Every assignment follows the same workflow:

Accept link → Open Codespaces → Write code → Run tests → Commit & push → Check score

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Step 1: Accept the Assignment

1. Your teacher gives you a GitHub Classroom link
2. Click the link and sign in to GitHub
3. GitHub creates a personal copy of the assignment repository for you
4. You will see a page that says "Your assignment repository has been created"
5. Click the link to go to your new repository

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Step 2: Open GitHub Codespaces

1. On your repository page, click the green Code button
2. Select the Codespaces tab
3. Click Create codespace on main
4. Wait for the environment to load (this takes about 30 seconds the first time)
5. You now have a full VS Code editor in your browser with Java and Maven pre-installed

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Step 3: Understand the Project Structure

Every assignment follows this Maven project structure:

Assignment-Name/
├── pom.xml                          <-- Maven config (DO NOT MODIFY)
├── src/
│   ├── main/java/
│   │   └── package/
│   │       └── ClassName.java       <-- YOUR CODE GOES HERE
│   └── test/java/
│       └── package/
│           └── ClassNameTest.java   <-- Tests (DO NOT MODIFY)
└── .github/
    └── workflows/
        └── classroom.yml            <-- Autograding config (DO NOT MODIFY)

You only edit the file in src/main/java/. Everything else is pre-configured.

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Step 4: Write Your Code

1. In the Codespaces file explorer (left sidebar), navigate to src/main/java/
2. Open the Java file (e.g., Unit1.java)
3. You will see method stubs — empty methods with // TODO comments
4. Implement each method according to the assignment README
5. Save your file (Ctrl+S or Cmd+S)

Example — a method stub before and after:

Before (what you start with):

public static int addIntegers(int a, int b) {
    // TODO: Return the sum of a and b
    return 0;
}

After (what you write):

public static int addIntegers(int a, int b) {
    return a + b;
}

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Step 5: Run Tests Locally

Open the terminal in Codespaces (Ctrl+`` or View → Terminal) and run:

mvn test

This compiles your code and runs all JUnit tests. You can run this as many times as you want — there is no limit.

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Step 6: Read Test Output

After running mvn test, you will see output like this:

All tests pass:

[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

Some tests fail:

[ERROR] testAddIntegers  Time elapsed: 0.003 s  <<< FAILURE!
AssertionError: expected:<5> but was:<0>

This tells you:

• The test testAddIntegers failed
• It expected the value 5
• Your method returned 0
• You need to fix your addIntegers method

Code does not compile:

[ERROR] COMPILATION ERROR
[ERROR] Unit1.java:[15,9] ';' expected

This tells you there is a syntax error on line 15 of Unit1.java. Fix the error and run mvn test again.

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Step 7: Commit and Push

Once you are happy with your code (or want to save your progress):

Using the Source Control Panel (Recommended)

1. Click the Source Control icon in the left sidebar (branch icon) or press Ctrl+Shift+G
2. You will see your changed files listed under "Changes"
3. Click the + icon next to each file to stage it (or click + next to "Changes" to stage all)
4. Type a commit message in the text box (e.g., "completed unit 1 methods")
5. Click the Commit button
6. Click Sync Changes to push to GitHub

Using the Terminal

git add -A
git commit -m "completed unit 1 methods"
git push

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Step 8: Check Your Autograded Score

1. Go to your repository on GitHub (not Codespaces)
2. Click the Actions tab at the top
3. Click the most recent workflow run
4. Look for the autograding step — your score appears there
5. The score is calculated from how many tests pass

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Practice Without Breaking Tests

Want to experiment with Java without affecting your assignment? Create a separate practice file:

1. Create Practice.java in the src/main/java/ directory (same folder as the assignment file)
2. Add a main method:

public class Practice {
    public static void main(String[] args) {
        // Your practice code here
        System.out.println("Hello from practice!");

        // Try out concepts
        int x = 10;
        int y = 3;
        System.out.println("Division: " + x / y);
        System.out.println("Remainder: " + x % y);
    }
}

3. Run it with:

javac src/main/java/*/Practice.java && java -cp src/main/java Practice

4. Delete Practice.java before your final push (it will not affect your tests, but keeps things clean)

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Common Code Patterns

Return a calculated value

public static int multiply(int a, int b) {
    return a * b;
}

Use an if-else to return different values

public static String getGrade(int score) {
    if (score >= 90) return "A";
    else if (score >= 80) return "B";
    else return "C";
}

Loop through an array

public static int sum(int[] arr) {
    int total = 0;
    for (int i = 0; i < arr.length; i++) {
        total += arr[i];
    }
    return total;
}

Build a string in a loop

public static String repeat(String s, int n) {
    String result = "";
    for (int i = 0; i < n; i++) {
        result += s;
    }
    return result;
}

Use ArrayList methods

public static void removeNegatives(ArrayList<Integer> list) {
    for (int i = list.size() - 1; i >= 0; i--) {
        if (list.get(i) < 0) {
            list.remove(i);
        }
    }
}

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Troubleshooting

Problem	Cause	Solution
"COMPILATION ERROR"	Syntax error in your code	Read the error message — it tells you the line number and what is wrong
"expected X but was Y"	Your method returned the wrong value	Check your logic. The test expected X but got Y
"NullPointerException"	You used a variable that is null	Make sure you initialized your variables before using them
"ArrayIndexOutOfBoundsException"	You accessed an invalid array index	Check your loop bounds — arrays are 0-indexed
Score did not update after push	You committed but did not push	Click "Sync Changes" in Source Control, or run git push
Codespace will not start	GitHub Codespaces quota reached	Delete old codespaces from github.com/codespaces
"package does not exist"	File is in the wrong directory	Make sure your file is in the correct src/main/java/package/ folder
Tests pass locally but fail on GitHub	You modified the test file	Revert changes to test files — the autograder uses the originals
"cannot find symbol"	Typo in method name or wrong import	Check spelling matches the assignment exactly
Build takes too long	First run downloads dependencies	Wait for it to finish — subsequent runs are faster
Terminal says "mvn: command not found"	Terminal session reset	Close and reopen the terminal, or restart the Codespace

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Tips for Success

1. Run mvn test after implementing each method — do not wait until the end
2. Read the error messages carefully — they tell you exactly what went wrong
3. Commit and push frequently so you never lose work
4. Do not modify test files, pom.xml, or anything in .github/
5. Method names, parameter types, and return types must match exactly
6. Start with the easiest methods first to build confidence
7. If you are stuck, re-read the assignment README — it has examples showing expected input and output
8. Use System.out.println() to debug — print variable values to see what your code is doing
9. Compare strings with .equals(), never with ==
10. If your code does not compile, you score 0 on everything — fix compile errors first

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FAQ

Q: Can I work on the assignment outside of Codespaces? Yes, if you have Java and Maven installed locally. But Codespaces is the easiest option since everything is pre-configured.

Q: How many times can I push? Unlimited. Push as often as you want. Each push triggers the autograder, and your most recent score is what counts.

Q: Can I see which tests passed and which failed? Yes. Run mvn test locally for detailed output, or check the Actions tab on GitHub for the autograder results.

Q: What if I accidentally delete a file? If you have not pushed the deletion, you can restore it with git checkout -- filename. If you have pushed, ask your teacher to help reset the repository.

Q: Do I need to write a main method? No. The JUnit tests call your methods directly. You do not need a main method unless you want one for your own testing.

Q: My Codespace expired. Is my work lost? If you committed and pushed, your code is safe on GitHub. Create a new Codespace from your repository and your code will be there. If you did not push, the work in the expired Codespace may be lost.

Q: Can I collaborate with other students? Each student has their own repository. You should write your own code. Ask your teacher about their collaboration policy.

Q: The autograder shows a different score than mvn test. Why? Make sure you did not modify the test files. The autograder uses the original tests. If you changed them locally, your local results may differ.

Q: How do I know which file to edit? The assignment README tells you. It is always in src/main/java/ — look for the file with // TODO comments.

Q: What does "BUILD FAILURE" mean? Either your code did not compile (check for syntax errors) or one or more tests failed (check the test output for details).

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View all assignments and scoring breakdowns at csplusplus.com/maven-tests

CS++ — AP Computer Science A — csplusplus.com