Strange '#filenames#' from emacs

Question

So after I modify one of my source files in emacs, when I list the files in the directory, there is a copy of the one I just modified with # signs on either side of it.

Example:

$ cd utility/
$ ls
FRCUtility.java
$ emacs FRCUtility.java 
$ ls
#FRCUtility.java#  FRCUtility.java

What does the # sign mean? Should I delete the file or keep it? A detailed explanation would be greatly appreciated.

Answer 1

The # signs are put in by emacs when it makes a temporary file. You can delete them if emacs doesn't do it for you.

Answer 2

It's an autosave file. It's there so you don't lose your changes to the file if emacs or your computer crashes. It disappears when you save the file.