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, 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 contain it.

Applications should not create their own file descriptors.

See Also

• FileInputStream
• FileOutputStream

Field Summary

public static final FileDescriptor	err	A handle to the standard error stream.
public static final FileDescriptor	in	A handle to the standard input stream.
public static final FileDescriptor	out	A handle to the standard output stream.

Public Constructor Summary

FileDescriptor() Constructs an (invalid) FileDescriptor object.

Public Method Summary

void	sync() Force all system buffers to synchronize with the underlying device.
String	toString() Returns a string containing a concise, human-readable description of this object.
boolean	valid() Tests if this file descriptor object is valid.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Fields

public static final FileDescriptor err

A handle to the standard error stream. Usually, this file descriptor is not used directly, but rather via the output stream known as System.err.

See Also

• System.err

public static final FileDescriptor in

A handle to the standard input stream. Usually, this file descriptor is not used directly, but rather via the input stream known as System.in.

See Also

• System.in

public static final FileDescriptor out

A handle to the standard output stream. Usually, this file descriptor is not used directly, but rather via the output stream known as System.out.

See Also

• System.out

Public Constructors

public FileDescriptor ()

Constructs an (invalid) FileDescriptor object.

Public Methods

public void sync ()

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.

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.

public String toString ()

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns

• a printable representation of this object.

public boolean valid ()

Tests if this file descriptor object is valid.

Returns

• true if the file descriptor object represents a valid, open file, socket, or other active I/O connection; false otherwise.