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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.

Since:
JDK1.0
See Also:
FileInputStream, FileOutputStream, java.net.SocketInputStream, java.net.SocketOutputStream

Field Summary
static FileDescriptor  err
A handle to the standard error stream.
static FileDescriptor  in
A handle to the standard input stream.
static FileDescriptor  out
A handle to the standard output stream.
 

Constructor Summary
 FileDescriptor()
Constructs an (invalid) FileDescriptor object.
 

Method Summary
void  sync()
Force all system buffers to synchronize with the underlying device.
boolean  valid()
Tests if this file descriptor object is valid.
 
Methods inherited from class java.lang.Object
 clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

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.
Constructor Detail

FileDescriptor

public FileDescriptor()
Constructs an (invalid) FileDescriptor object.
Method Detail

valid

public 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 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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