Checking if a file or directory exists in Java

Question

From this java tutorial by oracle:

Note that !Files.exists(path) is not equivalent to Files.notExists(path).

Why would they not be equivalent? it does not go any further in terms of explanation. Does anybody know more information about that? Thanks in advance!

Answer 1

!Files.exists() returns:

• true if the file does not exist or its existence cannot be determined
• false if the file exists

Files.notExists() returns:

• true if the file does not exist
• false if the file exists or its existence cannot be determined

Answer 2

As we see from Files.exists the return result is:

TRUE if the file exists; 
FALSE if the file does not exist or its existence cannot be determined.

And from Files.notExists the return result is:

TRUE if the file does not exist; 
FALSE if the file exists or its existence cannot be determined

So if !Files.exists(path) return TRUE means it not exists or the existence cannot be determined (2 possibilities) and for Files.notExists(path) return TRUE means it not exists (just 1 possibility).

The conclusion !Files.exists(path) != Files.notExists(path) or 2 possibilities not equals to 1 possibility (see the explanation above about the possibilities).