Instances of the file descriptor class serve as an opaque handle
to the underlying machine-specific structure representing an open
file, an open socket, or another source or sink of bytes. The
main practical use for a file descriptor is to create a
FileInputStream or FileOutputStream to
Applications should not create their own file descriptors.
Force all system buffers to synchronize with the underlying
device. This method returns after all modified data and
attributes of this FileDescriptor have been written to the
relevant device(s). In particular, if this FileDescriptor
refers to a physical storage medium, such as a file in a file
system, sync will not return until all in-memory modified copies
of buffers associated with this FileDescriptor have been
written to the physical medium.
sync is meant to be used by code that requires physical
storage (such as a file) to be in a known state For
example, a class that provided a simple transaction facility
might use sync to ensure that all changes to a file caused
by a given transaction were recorded on a storage medium.
sync only affects buffers downstream of this FileDescriptor. If
any in-memory buffering is being done by the application (for
example, by a BufferedOutputStream object), those buffers must
be flushed into the FileDescriptor (for example, by invoking
OutputStream.flush) before that data will be affected by sync.
SyncFailedException - Thrown when the buffers cannot be flushed,
or because the system cannot guarantee that all the
buffers have been synchronized with physical media.