Does git checkout update the staging area?

Question

The staging area can be updated via git reset, is there any case git checkout (or with many extra parameters) would update the staging area from new HEAD?

UPDATE: It seems git's behavior depends on whether you check out a file or a branch/commit.

1. If no file specified, it updates HEAD to point/switch to given branch/commit, and will warn and block the switch if there is any change in staged area and work tree. For example, git checkout DevBranch.
2. If file is specified but no branch/commit, it copies the specified file from staged area to work tree and doesn't touch stage area (doesn't update HEAD). For example, git checkout file.txt or git checkout -- file.txt.
3. If both branch/commit and file are specified, it updates the specified file in both stage area and work tree from given branch/commit (doesn't update HEAD). For example, git checkout DevBranch -- file.txt.

Answer 1

When you specify a branch or commit to git checkout, the staging area is indeed updated as well as the working directory. So, for example:

git checkout head~1 myfile.txt

will take the version of myfile.txt that is in head's parent and copy it to both the staging area and the working directory. If you do not specify a commit or branch, i.e.:

git checkout myfile.txt

then the contents of myfile.txt will be copied from the staging area to the working directory; the staging area itself is not changed.