Git

Today we will be learning git which is a tool for collaborating on code and other projects. It makes it easy to work multiple people on the same project.

Learning goals

• Understanding the git versioning ecosystem

• Installing git

• Creating repositories

• Commit / Add / Pull / Push

Git != Github

• Git is a versioning / Source Control Management (SCM) tool developed by Linus Torvalds

• “I really never wanted to do source control management at all and felt that it was just about the least interesting thing in the computing world (with the possible exception of databases ;^), and I hated all SCM’s with a passion” - Author of the Linux kernel

• Command Line tool to version & share codebases, built on the concept of repositories

• Repository = Code project

Github

• Online service that serves as remote repository for git repositories

• Acquired by Microsoft $7.5B

• Explore open source code

• Host to deploy simple web-applications

  • Portfolios: https://benna100.github.io/portfolio/

  • Git-books: https://behu.gitbook.io/java-first-semester/ External drive for text / files

Why?

• Share code base between developers / stakeholders

• Work distributed on a code base at the same time by:

  • Avoiding overwriting work done by others

  • Keep one source of truth Keep a version history

A world without version control

• Sending files over email/Facebook/whatever

• What happens when two developers have changed the same code?

• What is the newest version projectA_newest_1_new_old_new.java

Basic concept

Git basic

Initialising a repo

CleanShot 2021-09-03 at 13.48.55@2x

Comparison with saving a word document

Let's first start with an analogy: Saving word documents

1. You first make som changes that you would like to save

2. Now you press ctrl + s and save a word document. This is saved locally on your own computer

3. You can now take the document and sync to the cloud (save to the cloud)

4. The last step is if someone else has access to the document, their document will now sync with the newest changes

Hold these three steps in your head for later!

Working with git in the terminal

Steps to make this work

1. Create new repo on GitHub.com

2. Clone the repo down to you local machine using git clone GITHUB_REPO_LINK. Lets say it saved under c/users/benjamin/documents/kea/java-projects

3. Create a new IntelliJ project. Where you select the location, select the folder with the repo you just cloned down! In the above example that would be c/users/benjamin/documents/kea/java-projects

4. Now you should be able to use IntelliJ's github functionality!

Basic terminal usage

• pwd - Will tell where you are on your computer

• ls - Will list all the files and folder in your current folder

• cd - Will change directory fx cd java-exercises will change directory to java-exercises. You can also go up a level by writing cd ..

Initialising your repository

First you initialize a project on GitHub. Now you need to clone the project to your computer using the command git clone GITHUB_REPO_LINK

Adding a file to your repo

Now you have a repo locally on your computer, now you can start to add files to it.

git status

git status - shows you a status of your repository

When doing git status you will be able to see the changes that you have made to a repository. This is like the first step in the word analogy: making some change that we would like to save

git add

git add login.java - will add the changes in the login.java file

If we compare this to our word analogy. Imagine if we could make changes to a word document and decide which changes we would like to save. Fx save the changes where i added this header and that link. Instead of saving everything.

This is what git add does. You specify which changes you would like to save. In this case we add all the changes in the file called login.java

git commit

Now continuing with the word analogy, what if we could give the things we wanted to save a name. Fx save the changes i did where i wrote the intro and added the image and call this save wrote introduction

This is what is done with git commit. More specifically we say

git commit -m "Added login features"

This means:

• Commit all the change i added in the git add command (all the changes that i wanted to save)

• Give the commit a name called Added login features

• Commit all the changes that we said the git add command (adding the login.java file)

git push

Now we have want to take the commit containing the login.java file and push it to the cloud (GitHub.com). This we do with git push.

This is like step 3 in the word analogy

More specifically we say:

git push origin master

It means

• Push all the commit we have created

• Push it to the url origin (this is a shortcut for your repo link)

• master means push the changes on the master branch (you will learn about this later!)

git pull

To get the newest changes from git simply use git pull. This will pull down all the changes made to a repo so you now have those changes locally on your computer

Merge conflicts

Merge conflicts happens when two developers change the same line of code. Now you as a developer has to tell git which you want to keep and which you want to discard.

Exercises

Download git

https://git-scm.com/book/en/v2/Getting-Started-Installing-Git

Create a calculator

Remember to give the other collaborators access to your repo!

Go to your github repo. Click setting -> Manage access -> Invite collaborators.

If the GitHub repo already has

In your study groups you have to create a calculator collaboratively!

Each member should contribute (via git) with a calculator method. Fx an adder/subtractor/multiplication/whatever calculator method for your calculator.

The calculator program should take input from the console. Remember to make the program user-friendly with good print messages!

A good plan of action could be to that one person first creates a Java project and a Calculator.java file where all team members can work in!

Næste git opgave

Igen i jeres studiegrupper skal i hver lave en java klasse der har løsningen til en af de her opgaver. Des at der kommer til at være 4 java filer (hvis i er 4 i gruppen) med løsningen til hver af disse opgaver. I må gerne tage nogle andre opgaver fra fx de opgaver vi lavede igår omkring metoder

Hvor tit skal græsset slås

Om sommeren vokser græsset ca. 0,8 cm om dagen. Skriv en metode,der tager imod 2 input parametre: hvor langt græsset er lige nu og hvor højt det må være for at skulle slås.

Metoden skal beregne og returnere hvor mange dage der er til,at græsset skal slås næste gang. Hvor højt græsset er, når det skal slås, kan forstås på 2 måder.

1. Græsset skal overstige denne værdi,før vi starter græsslåmaskinen

2. Græsset skal slås,inden værdien overstiges

Du vælger selv hvilken løsning du vil implementere.

Benyt en Scanner til at få input fra brugeren, og udskriv resultatet på skærmen.

Kvadrat

Skriv en metode, der som parameter modtager et heltal. Metoden skal udskrive et kvadrat på skærmen svarende til heltallet. I det følgende eksempel er tallet 6 modtaget som parameter til metoden:

******
******
******
******
******
******

• Udvid metoden, så den også modtager et tegn, som er det tegn, som printes på skærmen

Proper case

Skriv en metode, der tager imod en sætning af ord med mellemrum imellem. Sætningen ændres efter følgende regler:

• Ord, som udelukkende er skrevet medstore bogstaver,skal ikke ændres.

• Ordpå mere end 3 bogstaver skal skrives med småt, dog med stort begyndelsesbogstav.

• Ord på max. 3 bogstaver skal skrives med småt

Sortering

Skriv en metode, der indlæser 5 tekststrenge fra tastaturet og udskriver dem på skærmen i alfabetisk faldende orden på skærmen. Hvis der indlæses:

abekat
musefælde
ananas
slut
solskin

skal der udskrives følgende på skærmen:

solskin
slut
musefælde
ananas
abekat