Chapter 11
The java.io Package

FileDescriptor

Name

FileDescriptor

Synopsis

Class Name:

java.io.FileDescriptor

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

The FileDescriptor class encapsulates system-specific handles for files and sockets. Instances of this class can be properly constructed only by native methods of other classes. In other words, you should not be constructing your own file descriptors. Currently, file descriptors are returned by the following methods:

DatagramSocketImpl.getFileDescriptor()
FileInputStream.getFD()
FileOutputStream.getFD()
RandomAccessFile.getFD()
SocketImpl.getFileDescriptor()

A file descriptor can be used in the constructors for FileInputStream, FileOutputStream, FileReader, and FileWriter.

Class Summary

public final class java.io.FileDescriptor extends java.lang.Object {
  // Constants
  public final static FileDescriptor err;
  public final static FileDescriptor in;
  public final static FileDescriptor out;
  // Instance Methods
  public native void sync();                     // New in 1.1
  public native boolean valid();
}

Constants

err

public final static FileDescriptor err

Description: The file descriptor for standard error. See System.err, which is constructed from this constant.

in

public final static FileDescriptor in

Description: The file descriptor for standard input. See System.in, which is constructed from this constant.

out

public final static FileDescriptor out

Description: The file descriptor for standard output. See System.out, which is constructed from this constant.

Instance Methods

sync

public native void sync() throws SyncFailedException

Availability

New as of JDK 1.1

Throws

SyncFailedException: If synchronization cannot be accomplished.

Description

This method causes the underlying device to be updated to a current state, which typically involves asking the operating system to flush its buffer. For example, if this FileDescriptor refers to a file on a physical disk, the disk is physically updated to reflect the current state of the object this descriptor represents. This method allows an application to put a device in a known state, which could be useful for transaction processing.

valid

public native boolean valid()

Returns

true if the FileDescriptor represents a valid, open device; false otherwise.

Description

This method returns a boolean value that indicates the validity of the file descriptor.

Inherited Methods

Method	Inherited From	Method	Inherited From
`clone()`	`Object`	`equals(Object)`	`Object`
`finalize()`	`Object`	`getClass()`	`Object`
`hashCode()`	`Object`	`notify()`	`Object`
`notifyAll()`	`Object`	`toString()`	`Object`
`wait()`	`Object`	`wait(long)`	`Object`
`wait(long, int)`	`Object`