Lab 2: Branching and Merging

The main topic of this first lab activity is branching and merging in git.

Resources and Acknowledgements

https://www.atlassian.com/git/tutorials/using-branches contains an excellent, detailed walkthrough of the steps we will be going through in the lab. We encourage you to use it as a reference as needed. The short video (about 4 minutes) is well worth a quick view in the link above.

The first coding part in this activity is (very loosely) based on a common problem encountered in problems posted on https://projecteuler.net/archives which is another interesting source of challenging programming problems. You might also recognize that the multiples of 3 and 5 problem from last week came from there. If you are looking for challenges, definitely check it out.

The partial cake recipes are courtesy ChatGPT.

TASK 0: Fork this repo

Note: If you are in lab, your TA will share a different URL for you to fork from, so that you can make pull requests to that repo during the Task 3 activity during the lab.

During lab, you should not fork directly from https://github.com/CSC207-2023F-UofT/Lab2. If you miss the lab and work on this after, you should use this URL though.

• Make a fork of this repo and clone a local copy (as you did in Lab 1).
  • Important: make sure to uncheck the option to only fork the main branch, as the repo contains some branches you will use in this lab.

TASK 1: Your first branch

• Create and checkout a new branch called task_1 using either IntelliJ or the Terminal:
  • IntelliJ: Git -> New branch...
  • Terminal: git checkout -b task_1
  • After, you can check git status or the Log tab of the Git tool window in IntelliJ to see that you are now on the task_1 branch.
• Open the TODO tool window (View -> Tool Windows -> TODO) and click on the TASK 1 TODO listed.
• Complete the TASK 1 TODO and commit your changes to this file (checking off the completed items so far) and DataTypes.java (remove the word TODO and your bug fix).
  • talk to those around you or your TA, then see the hints at the bottom of the readme if you get stuck.
• Now, we'll merge the task_1 branch back into main. When merging, you need to be currently on the branch you are trying to merge into, so we'll first checkout the main branch:
  • IntelliJ: Git -> branches... -> main -> Checkout
  • Terminal: git checkout main Note: everything we've done has been local to our repository and have not pushed anything yet.
• We are back on main, so we can now do the merge and complete our work!
  • IntelliJ: Git -> Merge... -> task_1 -> Merge
  • Terminal: git merge task_1

You should now see the changes you had made are also in the main branch.

• Now, we'll want to clean up since we are done with our task_1 branch.

  • IntelliJ: Git -> branches... -> task_1 -> Delete
  • Terminal: git branch -d task_1

• Last step, we'll push our changes to the remote repository to share our work! (As we did in Lab 1.)

  • we suggest you check off this last item, commit that change (just right on main is fine; no need to branch for this little step), then push your code. Check GitHub to ensure you can see your changes.

And that's it for Task 1! You might be wondering about how we are supposed to get someone else to review and approve our changes before we commit and push our changes to the main branch of our remote repository, since everything we just did was local. We'll explore how to do precisely that by pushing our branch to our remote repository and making a pull request shortly, but first, we'll talk about merge conflicts and how to resolve them.

Tip: In the Git tool window, you can open the Console tab to see the underlying git commands it is performing when you ask IntelliJ to perform various git operations for you.

TASK 2: Let's bake a cake!

Alice and Bob are planning to bake a cake, but can't agree on which recipe to use. They had started working on the recipe in recipe.md together, and then each filled in the details of what they felt would make the most delicious cake! You'll notice that your repository already has two branches called alice and bob.

• Checkout the alice branch.

• Attempt to merge the bob branch into the alice branch using either IntelliJ or the Terminal.

  • You will be prompted to resolve a merge conflict. To do this, you will need to pick and choose which parts of each recipe to keep.
  • Read what either git or IntelliJ tells you in order to complete the merge process.
    • If you do the merge through the Terminal, you will need to edit recipe.md to remove all of the merge conflict symbols which git has added to your file. Once done, you will need to git add the recipe.md file and git commit to finish the merge.

• Once the merge is complete, delete the bob branch.

• Finally, checkout the main branch and merge the alice branch in (as we did previously).

Now, you are almost ready to share your recipe with the remote!

TASK 3

• Checkout a new branch called task_3.
• Commit any changes that you want to recipe.md to improve the recipe.
• While still on the task_3 branch, push your code to your remote repository on GitHub.
• Go to GitHub and you will see an option to make a pull request to the original repo. Make a pull request and see that it shows up in the original repository that you forked.

Since others will also be making pull requests, we won't actually accept any of them for now, but you'll get lots of practice with pull requests in the next task and throughout the rest of the course!

We're now ready to dive into a collaborative coding challenge.

Proceed to the second lab activity!

Hints and Tips

TASK 1 TODO: Hints

• Hint 1: you only have to change one line of code
• Hint 2: unlike Python, an int has a maximum value that it can store (see Integer.MAX_VALUE). also see https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

TASK 2 (and possibly other places): Note about Unsaved local changes

If you have any local changes which you haven't committed, git will refuse to do certain operations which would result in the loss of your changes. It will advise you on what you should do in order to proceed. If you have any changes you want to keep, you will typically want to commit those changes.

Note: you can use git status or Git -> commit... to see the status of your files to check which ones have changes not yet committed.

TASK 3 Additional Note

When making a pull request, there may potentially be merge conflicts to resolve, as we had seen in the previous task. GitHub as additional information about how its interface helps facilitate resolving such conflicts:

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/addressing-merge-conflicts/resolving-a-merge-conflict-on-github