Concurrent file write in Java on Windows

What happens when you concurrently open two (or more) FileOutputStreams on the same file? The Java API says this: Some platforms, in particular, allow a file to be opened for writing by only one FileOutputStream (or other file-writing object) at a time. I'm guessing Windows isn't such a platform, because I have two threads that read some big file (each one a different one) then write it to the sam