FULL PRODUCT VERSION :
java version "1.8.0_144"
Java(TM) SE Runtime Environment (build 1.8.0_144-b01)
Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64 x86_64

A DESCRIPTION OF THE PROBLEM :
Example:
I have a "/tmp/file.txt" and "/tmp/file.txt.tmp".

I would expect that java command
"Files.move(originalPath, finalPath, StandardCopyOption.ATOMIC_MOVE)"
would only succeed when both files have the same hash and filesize (when the files are identical).

When the files differ I would expect a FileAlreadyExistsException.

However the FileAlreadyExistsException is only thrown when ATOMIC_MOVE is not enabled.

In my opinion the java API is not very clear in this respect. The java API states: "If the target file exists then it is implementation specific if the existing file is replaced or this method fails by throwing an IOException."

Possible solutions:
- change the implementation that it matches the expectation
- more understandable java api, so that it mentions the fact that FileAlreadyExistsException might not be thrown in some implementations.


REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
Not using Atomic move option.