Git checkout does not change anything

I had this issue when I tried to switch temp to another branch from the master branch and when I would change something on that temp page and without committing the changes I would checkout the master branch again, it actually merged all the changes from the TEMP branch into MASTER.

ANSWER:

Whenever you checkout to a TEMP branch, COMMIT your changes. That way if you commit them on the TEMP branch and checkout MASTER again, it will work as supposed.

Here is an example of how to use git and branches.

$ git branch
* master
  organize

$ git branch networking
$ git checkout networking

$ git branch
  master
* networking
  organize

Now Master has been updated many times since anyone has done anything on networking

$ git pull origin networking
From github.com:dlundquist/Asteroids
 * branch            networking -> FETCH_HEAD
CONFLICT (rename/delete): Rename src/ServerClientThread.java->src/ServerConnectionThread.java in 92d5b7c4e7c4110803eabf5d5152e7f2a337d722 and deleted in HEAD
Auto-merging src/Actor.java
Auto-merging src/Asteroids.java
CONFLICT (content): Merge conflict in src/Asteroids.java
Auto-merging src/BasicWeapon.java
CONFLICT (content): Merge conflict in src/BasicWeapon.java
CONFLICT (delete/modify): src/DedicatedServer.java deleted in HEAD and modified in 92d5b7c4e7c4110803eabf5d5152e7f2a337d722. Version 92d5b7c4e7c4110803eabf5d5152e7f2a337d722 of src/DedicatedServer.java left in tree.
Auto-merging src/MainMenu.java
CONFLICT (content): Merge conflict in src/MainMenu.java
CONFLICT (delete/modify): src/NetworkClientThread.java deleted in HEAD and modified in 92d5b7c4e7c4110803eabf5d5152e7f2a337d722. Version 92d5b7c4e7c4110803eabf5d5152e7f2a337d722 of src/NetworkClientThread.java left in tree.
CONFLICT (delete/modify): src/NetworkUpdate.java deleted in HEAD and modified in 92d5b7c4e7c4110803eabf5d5152e7f2a337d722. Version 92d5b7c4e7c4110803eabf5d5152e7f2a337d722 of src/NetworkUpdate.java left in tree.
Auto-merging src/ScenePanel.java
CONFLICT (content): Merge conflict in src/ScenePanel.java
Auto-merging src/Shield.java
CONFLICT (content): Merge conflict in src/Shield.java
Auto-merging src/Sprite.java
Auto-merging src/TripleShotWeapon.java
Auto-merging src/Weapon.java
Automatic merge failed; fix conflicts and then commit the result.
mjolnir:Asteroids Durandal$ git status
# On branch networking
# Changes to be committed:
#
#   modified:   src/Actor.java
#   modified:   src/Sprite.java
#   modified:   src/TripleShotWeapon.java
#   modified:   src/Weapon.java
#
# Unmerged paths:
#   (use "git add/rm <file>..." as appropriate to mark resolution)
#
#   both modified:      src/Asteroids.java
#   both modified:      src/BasicWeapon.java
#   deleted by us:      src/DedicatedServer.java
#   both modified:      src/MainMenu.java
#   deleted by us:      src/NetworkClientThread.java
#   deleted by us:      src/NetworkUpdate.java
#   both modified:      src/ScenePanel.java
#   added by them:      src/ServerConnectionThread.java
#   both modified:      src/Shield.java

Woah, git is really mad. It looks like Master is too far ahead of Networking for git to do all the work for me.

$ git reset --hard networking
HEAD is now at 20d6ee8 done tweaking game on the main branch.  Fixed a few bugs with the TripleShotWeapon.  Rebalanced the gameMechanics() in Asteroids to increase the difficulty as the levels increase.
mjolnir:Asteroids Durandal$ git status
# On branch networking
nothing to commit (working directory clean)

Ok, now I am "back in time" when networking last pushed to origin. But I really should go back and merge with Master now before I do any work. Other wise it will be even hard to merge.

Time spent merging files

$ git add (insert conflict resolved files here)
$ git commit -a -m "Merged networking with master"
$ git checkout master
$ git branch
* master
  networking
  organize

Now lets apply our changes.

$ git merge networking
Already up-to-date.

You might want to do this if you like the "Yeah!"

$ git merge origin networking
Already up-to-date. Yeeah!

Push our changes to the world

$ git push origin master

I like to explain git in common language. Answer: its because of the assumption that changing branches (checkout) will get you to another "workspace". Git doesn't do that (altough it feels more natural, and many have this misunderstanding).

Instead, branches are like tags, so to speak. So you can dance around branches, do some work, modify things, dance around again, and then commit. Then, the commit will be at the last branch you went to! The checkout only changes the "tag"/branch you'll use, period.

UPDATE after Martas's comment

This applies to when your branch and your master are synced (regarding tracked files), or with untracked files. If in fact they are in different states, when you checkout then files and folders will actually disapear and reappear. If you have changes tracked but not commited, then git will actually abort checking out, and you have to either commit or stash them.

Please check if you have write access or not. This error comes up with read only access to the repository.