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# Class java.io.FileDescriptor

    java.lang.Object
       |
       +----java.io.FileDescriptor

public final class FileDescriptor
extends Object

Instances of the file descriptor class serve as an opaque handle to the underlying machine-specific structure representing an open file or an open socket.

Applications should not create their own file descriptors.

See Also:
  FileInputStream, FileOutputStream, SocketInputStream, SocketOutputStream

##

err
  A handle to the standard error stream.
in
  A handle to the standard input stream.
out
  A handle to the standard output stream.

##

FileDescriptor()

##

sync()
  Force all system buffers to synchronize with the underlying device.
valid()
  Tests if this file descriptor object is valid.

##

in

     public static final FileDescriptor in

  A handle to the standard input stream.

out

     public static final FileDescriptor out

  A handle to the standard output stream.

err

     public static final FileDescriptor err

  A handle to the standard error stream.

##

FileDescriptor

     public FileDescriptor()

##

valid

     public native boolean valid()

  Tests if this file descriptor object is valid.

  Returns:
    `true` if the file descriptor object represents a valid, open file or socket; `false` otherwise.

sync

     public native void sync() throws SyncFailedException

  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 FileDesecriptor 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.

  Throws: SyncFailedException
    Thrown when the buffers cannot be flushed, or because the system cannot guarantee that all the buffers have been synchronized with physical media.

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