How can I (simply) undo changes to a file in GIT?

Question

lets say I have a file, and lets call it "A.java".

....I don't have any hash tag ids / etc... I just want to go back to the file in the state before I screwed it up .

Answer 1

git reset --hard will reset all files in the repository back to their state. git checkout A.java will reset just that file.

Answer 2

git checkout -- <filename>

this will checkout your file to the master repository.

Check this out for more information

Difference between "git checkout <filename>" and "git checkout -​- <filename>"

Answer 3

git checkout -- A.java
git pull #if you need to pull changes from the remote.

This assumes you haven't already tried to pull and are in the middle of a merge.