FAQ #

Each assignment will have an FAQ linked at the top. You can also access it by adding “/faq” to the end of the URL. The FAQ for Lab 1 is located here.

Introduction #

In this lab, we will prepare ourselves to succeed in the course by setting up our computers, so that we can use them to work on assignments. We will also write a small Java program to learn the assignment workflow.

Goals and Outcomes #

In this lab, you will set up your computer for the class. You will also read and understand a short Java program, and identify its logical flaws. By the end of this lab, you will:

• Have a computer that you can use to work on class assignments.
• Be able to get the starter code for an assignment.
• Have written and submitted a small Java program.

Welcome to CS 61B! #

We’re very excited to work with you this term! Before we can get started, you’ll need to have a computer that you can work on assignments on. In this class, you’ll be using real-world tools, which means that you’ll likely run into real-world problems. These are hard problems, and software engineers run into them every day! Don’t be discouraged, and make sure to ask for help if you’re stuck!

We highly recommend attending a lab section, and asking for help during lab section. If you’re working outside of a lab section, you can ask on Ed or attend office hours.

Partners #

Labs in CS 61B are solo. This means that you will need to write and submit your own code. For Lab 1 in particular, you will need to set up your own computer.

However, we strongly encourage working together with other students! In-person lab sections are an excellent place to find groups.

Personal Computer Setup #

Installing Software #

Installation will vary, depending on your operating system.

• Windows instructions
• macOS instructions
• Linux instructions

The Terminal #

How to use the Terminal #

In CS 61B, we will be using the terminal extensively to work with git. The terminal also has some other commands that allow you to work with folders or files. Here’s a list of the most important commands for CS 61B:

• cd: change your working directory

  cd hw
  

  This command will change your directory to hw.

• pwd: present working directory

  pwd
  

  This command will tell you the full absolute path for the current directory you are in if you are not sure where you are.

• ~: shorthand for your home directory

• .: shorthand for your current directory

  cd .
  

  This command will change your directory to the current directory (aka. do nothing).

• ..: shorthand for one parent directory above your current directory

  cd ..
  

  This command will change your directory to its parent. If you are in /workspace/day1/, the command will place you in /workspace/.

• ls: list files/folders in a directory

  ls
  

  This command will list all the files and folders in your current directory. You can also use ls <directory> to list the contents of a different directory – try ls ..!

• mkdir: make a directory

  mkdir [dirname]
  

  This command will make a new directory within the current directory called dirname.

• touch: create a new file

  touch [filename]
  

  This command will create a file within the current directory called filename.

• rm: remove (delete) a file

  rm [file]
  

  This command will remove file from the current directory. It will not work if file does not exist.

  rm -r [dir]
  

  This command will remove the dir directory recursively. In other words, it will delete all the files and directories in dir in addition to dir itself. Be careful with this command!

• cat: display the contents of a file

  cat [file]
  

  This command is useful for inspecting the contents of files in the terminal without having to open them in a program. It is not as useful for large files (which can clutter the terminal) or non-text files (which will likely output gibberish).

• cp: copy a file

  cp lab1/original lab2/duplicate
  

  This command will copy the original file in the lab1 directory and and create a duplicate file in the lab2 directory.

• mv: move or rename a file

  mv lab1/original lab2/original
  

  This command moves original from lab1 to lab2. Unlike cp, mv does not leave original in the lab1 directory.

  mv lab1/original lab1/newname
  

  This command does not move the file but rather renames it from original to newname.

Here are some other useful tricks when working in a terminal.

• Your shell can complete file names and directory names for you with tab completion. When you have an incomplete name (for something that already exists), try pressing the tab key for autocomplete or a list of possible names.

• You can copy-paste into the terminal. This is straightforward on Mac, but on Windows, right-click to copy and paste highlighted text.

• If you want to run the same command used recently, press the up arrow key on your keyboard until you see the correct instruction. If you go too far, use the down key to go back. This saves typing time if you are doing repetitive instructions.

Terminal Test Run #

Let’s ensure that everything is working.

1. First open up your terminal. Check that git is a recognized command by typing the following command:

   git --version
   

   The version number for git should be printed. If you see “git: command not found”, or similar, try opening a new terminal window, restarting your computer, or installing git again.

2. Second, let’s check that javac and java are working. javac and java allow Command Line Compilation, or in other words, the ability to run Java programs directly from the command line. In practice, most developers run Java programs through an IDE like IntelliJ, so we won’t be using command line compilation this semester other than testing your setup.

   Start by running the following commands at your terminal.

   mkdir ~/temp
   cd ~/temp
   

   1. Then, open your operating system’s file explorer in this directory. You can do this from the command line:

      • Mac: open .
      • Windows: explorer .
      • Ubuntu: gnome-open .

   2. In this newly opened directory, create a file HelloWorld.java with these contents:

      public class HelloWorld {
          public static void main(String[] args) {
              System.out.println("Hello world!");
          }
      }
      

      Note that in addition to the file finder or explorer, you are able to create a file using the touch in the terminal; try creating the file using touch HelloWorld.java from the terminal! Then, open the file using your favorite text editor and copy-paste the code.

   3. In your terminal, enter ls (list the files/folders in this directory). You should see HelloWorld.java listed.

   4. Run javac HelloWorld.java. If this produces any output, then something may be wrong with your setup. Try opening a new terminal window or restarting your computer. If that still doesn’t work, see the Troubleshooting section under the directions for your operating system.

   5. Type ls, you should see both HelloWorld.java and a freshly created HelloWorld.class (the javac command created this file).

   6. Run java HelloWorld. It should print out “Hello world!” for you. If it didn’t, something is wrong with your setup!

   7. You’re done! You can also delete the “temp” folder and its contents as you please.

The screenshot below shows what we’re hoping for when we do the above steps. If you see something similar to this, your terminal setup is complete.

GitHub and Beacon #

Instead of bCourses, CS 61B uses an in-house system for centralizing your grades and student information called Beacon.

In this section, we’ll set up your Beacon account as well as your CS 61B GitHub repository (“repo”), which you will need to submit all coding assignments.

Account Setup #

1. Create an account on GitHub. If you already have an account, you do not need to create a new one.
2. Go to Beacon and follow the steps to complete your GitHub repository registration. You must be logged in to your Berkeley account to complete the Google Form syllabus quiz.
3. After completing all of the steps, you should receive an email inviting you to collaborate on your course GitHub repository. Accept the email invitation to receive access to your course repository. This email will be sent to the email that you used to create your GitHub account, which may not necessarily be your Berkeley email.

Your Repository #

Your repository will have a name containing a number that is unique to you. For instance, if your repo is called “sp23-s1”, you’ll be able to visit your private repository at https://github.com/Berkeley-CS61B-Student/sp23-s1 (when logged into GitHub). Your student number is not “1”, so this link will not work for you. Replace “1” with your own number to see your repo on GitHub.

Additionally, the instructors, TAs, and tutors will be able to view your repository. This means you can (and should!) link to your code when asking private debugging questions in Ed or Gitbugs. No other students will be able to view your repository.

Git #

Git Basics #

In this course, you’ll be required to use the Git version control system, which is nearly universal out in the real world. Since the abstractions behind it are fairly tricky to understand, don’t be worried if you encounter significant frustration as you learn to use it.

Setting Up Git #

Before we use git, we have some short commands to configure it appropriately.

First, set the name and email that git will use with these two commands:

git config --global user.name "<your name>"
git config --global user.email "<your email>"

Set git’s default branch name:

git config --global init.defaultBranch main

Set the “merge strategy”:

git config --global pull.rebase false

We’ll also change the text editor associated with git. Sometimes, git needs your help when inputting things like commit messages, so it will open a text editor for you. The default editor is vim, which is notoriously difficult to use. We recommend nano for this course, but you’re free to use whatever you’d like.

Follow the instructions here. This will configure Git’s default editor (make sure that you follow the correct instructions for your operating system).

Git Exercise #

Now you’re ready to start using git! Your next task is to work through a small git workflow by setting up a repository and making a couple commits. At the end, you will need to be checked off by filling out the form linked on Beacon.

If you need help with creating directories, creating files, changing directories, etc., refer back to How to use the Terminal.

Section C of the Using Git Guide will also be helpful for this exercise.

1. Create a directory called lab01-checkoff. You can put this directory anywhere on your computer (unless you have already cloned your sp23-s*** repository, in which case, you should not put this directory inside of your sp23-s*** repo).
2. Move into the lab01-checkoff directory, and initialize a git repository in this directory.
3. Create a file called 61b.txt in any way you’d like. In this text file, add the text “61b version 1” into it.
4. Create another file called 61bee.txt in any way you’d like. file, add the text “61bee version 1” into it.
5. Begin tracking only 61b.txt, and create a new commit containing just this file, with the following commit message: Add 61b.txt.
6. Make a modification in 61b.txt by changing the text in the file to: “61b changed to version 2”.
7. Make another commit, this time containing both 61b.txt and 61bee.txt. The commit message should be: Update 61b.txt and add 61bee.txt.

8. Make one more modification to 61b.txt by changing the text in the file to: “61b changed to version 3”. Don’t commit this version.

   At this point, if you were to type in git status and git log, you’d see something like the following:

9. Using git only, restore 61b.txt to the version in the most recent commit.
10. Using git only, restore 61b.txt to the version in the first commit.

Be sure to save this repository and directory until you complete the asynchronous checkoff form on beacon and obtain a magic word.

Git and Remote Repos #

First, read the Remote Repositories section of the Using Git Guide.

In this course, you’ll be required to submit your code using git to your course GitHub repository that you created in Account Setup. This is for several reasons:

• To spare you the incredible agony of losing your files.
• To submit your work for grading and to get results back from the autograder.
• To save you from the tremendous anguish of making unknown changes to your files that break everything.
• To ensure that we have easy access to your code so that we can help if you’re stuck.
• To dissuade you from posting your solutions on the web in a public GitHub repository. This is a major violation of course policy!
• To expose you to a realistic workflow that is common on every major project you’ll ever work on in the future.

Setting up your Git Repository #

Clone your sp23-s*** Git Repository #

Navigate to the spot in your folders on your computer that you’d like to start your repository. In the example below, we’re assuming you want all your stuff in a folder named cs61b, but you can pick a different name if you’d like.

cd cs61b

In order to clone your GitHub repo, your local computer needs to setup GitHub access credentials. Go to github.com, sign in with your GitHub username and password, and click the user profile in the top right corner, then click to “Settings”:

Then click on the “developer settings” tab:

and generate a classic personal access token.

• Give a note to the token so you remember what it’s for
• Set the token to have no expiration
• Give the token “repo” permissions

Then, when you’re ready, scroll to the bottom of the page and press the green “Generate Token” button.

After obtaining a token, enter the following command to clone your GitHub repo. Make sure to replace the *** with your repository number from Beacon.

git clone https://github.com/Berkeley-CS61B-Student/sp23-s***.git

You might be prompted for a username and password:

Enter your GitHub username. For the password, use the token you generated. When you copy-paste, it won’t show anything – this is expected.

You might instead be prompted to sign in in a browser window for “Git Credential Manager,” or not be prompted to sign in at all. As long as you’re able to clone the repo successfully, the exact sign in method does not matter.

Move into your newly created repo!

cd sp23-s***

Make sure that we’re working with the branch name we expect, main:

git branch -M main

Add the skeleton remote repository. We add starter code for the assignments to skeleton, and you will pull from it.

git remote add skeleton https://github.com/Berkeley-CS61B/skeleton-sp23.git

Listing the remotes should now show both the origin and skeleton remotes.

git remote -v

Getting the Skeleton #

Pushing to GitHub #

Open the file lab01/magic_word.txt in a text editor, and edit it to contain the magic word obtained during the git exercise.

Now stage and commit magic_word.txt (make sure you’re in your repo!).

git add lab01/magic_word.txt
git commit -m "Added Magic Word"

Right now, the modified magic_word.txt is only on your computer. We want to push these changes to the GitHub repository so that your changes can be seen by us and Gradescope. Push these changes to the main branch on the origin remote repo.

git push origin main

You can verify that this was successful by checking your repository online on GitHub’s website. It should contain the updated magic_word.txt file. If it doesn’t, make sure that your add and commit were successful. In particular, make sure that you are in your repo, sp23-***.

Our work is now on GitHub, and ready to submit!

Submitting to Gradescope #

Although we use GitHub to store our programming work, we use Gradescope to actually grade it. The last step is to submit your work with Gradescope, which we use to autograde programming assignments.

Setting Up Java Libraries #

Like in Python, we sometimes want to use libraries that others wrote. Java dependency management is a bit of a mess, so we instead provide a git repo that contains all the dependencies that we will use in this course.

Then, run:

git clone https://github.com/Berkeley-CS61B/library-sp23

Below is shown the directory structure of library-sp23. Look inside the folder using ls library-sp23 and make sure you see the .jar files listed below. There are many more, but we only list the first few. If you’re using your operating system’s file explorer, the jar part might not show up in the filenames, and that’s OK.

library-sp23
├── algs4.jar
├── animated-gif-lib-1.4.jar
├── antlr4-runtime-4.11.1.jar
├── apiguardian-api-1.1.2.jar
└── ...

IntelliJ Setup #

IntelliJ is an Integrated Development Environment or IDE. An IDE is a single program which combines typically a source code editor, tools to compile and run code, and a debugger. Some IDEs like IntelliJ contain even more features such as an integrated terminal and a graphical interface for git commands. Finally, IDEs also have tools like code completion which will help you write Java faster.

We highly recommend using IntelliJ. Our tests are written to run in IntelliJ, and we will explicitly use its debugger in later labs. Additionally, IntelliJ is an industry-standard tool that you will almost certainly encounter if you work with Java again in the future.

We will assume that you are using IntelliJ, and will not offer support for other editors, including VSCode.

Before continuing, make sure that you have completed all above tasks besides the git exercise:

1. You have installed Java 17 or higher.
2. You have successfully created your local repo for the class on your own machine. This is the sp23-s*** repository you earlier.
3. You have pulled from the skeleton, and you have a lab01 directory.

Installing IntelliJ #

1. Download the Community Edition of IntelliJ from the JetBrains website. As a student you can actually get a student license for the Ultimate version, but there are not any additional features that we will use for this class. It is recommended and assumed that you proceed with the Community Edition.

2. After selecting the appropriate version for your OS, click download and wait a few minutes for the file to finish downloading.

3. Run the installer. If you have an older version of IntelliJ, you should uninstall it at this time and replace it with this newer version.

Installing Plugins #

Open IntelliJ. Then follow the steps below.

Make sure you’re running IntelliJ Version 2021.2 or later before continuing. This is because we will use Java 17. We are using IntelliJ Version 2022.3. Older versions may also work but we haven’t tried them ourselves.

1. In the Welcome window, click the “Plugins” button in the menu on the left.

   

2. On the window that appears, click “Marketplace” and enter “CS 61B” in the search bar at the top. The CS 61B plugin entry should appear. If you click the autocomplete suggestion, a slightly different window from what is shown below may appear – this is okay.

3. Click the green Install button, and wait for the plugin to download and install.

   

   If you have the plugin installed from a prior term, make sure to update it.

4. Now, search for “Java Visualizer”, and click the green Install button to install the plugin.

   

5. Restart (close and reopen) IntelliJ.

For more information on using the plugins, read the plugin guide. You don’t have to read this right now.

Creating Projects #

Once you’ve done this, you should see at least these three files in the left pane:

• magic_word.txt, which should contain the magic word you added.
• src/Arithmetic, a Java file which contains your first programming exercise.
• tests/ArithmeticTest, another Java file which will check that Arithmetic is implemented correctly.

When you open Arithmetic and ArithmeticTest, you should not see any red text or red squiggles.

IntelliJ Test #

To test if everything is working correctly, run the Arithmetic class by opening the file, clicking on the green triangle next to public class Arithmetic, then clicking “Run ‘Arithmetic.main()’”.

You should see a console pop up, prompting you to enter a number:

If you follow the prompts, you will (probably) see something wrong! Don’t fix it yet.

Testing Your Code #

While we could run the Arithmetic file again and again to check that our code works correctly, it would take a lot of time to type into the program each time, and manually check that the output is correct. Instead, we use tests.

Open ArithmeticTest, and click the green triangle(s) next to the public class ArithmeticTest. This will run the tests that we have provided in this assignment. At this point, you will see the following:

The green checkmark () indicates tests that you have passed, while the yellow X () indicates tests that you have failed. Don’t worry about the doubled output; this is a strange quirk of IntelliJ.

Saving Your Work using Git and GitHub #

As you are making changes to your code, it is good practice to save your work often. We have briefly discussed the commands, but now we will explain how they should be used in practice. In the case that you ever want to go back to another version of your code, it is better to have more options to roll back to. The next set of instructions will talk you through git’s version of saving work through snapshots of your file system called commits.

1. After you have made some changes to the code within our local repository, git will take notice of these changes. To see the current state of your local repository, use the command git status. Run this and try to interpret the results. Do they make sense to you or do they match your intuition? It is a good habit to run this before running other git commands to know what the state of things are.

2. To save work that we have completed on a file, we first stage the file, and then we can commit it. We stage a file with the command git add. This does not save the file, but it marks it to be saved the next time you commit. The two below commands show what saving work looks like in a git repository. For git add depending on what directory you are in, the path to the file you are adding might differ (use git status to see the path).

   The -m "Completed Arithmetic.java" part of the commit command specifies a message to be attached to this snapshot. You should always have a commit message to identify what exactly happened in this commit. As an example workflow:

   git add lab01/src/Arithmetic.java
   git commit -m "lab01: Completed Arithmetic.java"
   

   If you run git status, you will see that Your branch is ahead of 'origin/main'. You will also see that the staged changes are no longer staged, and are instead committed. If you haven’t edited since staging, you shouldn’t have any changes not staged for commit.

3. We want to push these changes to the GitHub repository so that your changes can be seen by us and Gradescope. Your changes will also be available to pulled if you had your repo initialized in other places or other computers.

   git push origin main
   

   git status will now show that Your branch is up to date with 'origin/main'.

Basically, right when you sit down to work in your repository, first git pull to make sure you are starting with the most recent code. While you are working, frequently commit. When you are finished, git push so all your changes are uploaded and ready for you to pull again next time.

Deliverables #

As a reminder, this assignment has an FAQ page. There are two required files, all inside the lab01 directory:

magic_word.txt

You should have received the correct magic word from completing the git checkoff.

Arithmetic.java

You should have fixed the bug so that the tests pass. We check this file with an autograder! For this lab, the autograder tests are the same as the ones you have on your computer.

Be sure to submit again according to the submission section, so that you submit your completed lab. Congratulations on finishing your first CS 61B lab!

Optional: Josh Hug’s Color Scheme IntelliJ Download #

Per Josh Hug:

I’m not a big fan of the default IntelliJ colors, so I made my own color scheme, which is a very close imitation of the extremely good Sunburst theme for Sublime. To use my theme, download hug_sunburst, and import it using the “File → Manage IDE Settings → Import Settings” option in IntelliJ. You might end up with large text, which I use for recording videos. To adjust the size of the font in Intellij to your liking, see this link.