FileDescriptor

public final class FileDescriptor
extends Object

java.lang.Object
↳	java.io.FileDescriptor

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:

Summary

Fields
`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 constructors
`FileDescriptor()` Constructs an (invalid) FileDescriptor object.

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

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Fields

err

Added in API level 1

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

in

Added in API level 1

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

out

Added in API level 1

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

FileDescriptor

Added in API level 1

public FileDescriptor ()

Constructs an (invalid) FileDescriptor object.

Public methods

sync

Added in API level 1

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.

valid

Added in API level 1

public boolean valid ()

Tests if this file descriptor object is valid.

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