# FileDescriptor

public final class **FileDescriptor** extends [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)  
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

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileInputStream.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileOutputStream.html`

### Field Summary

|---|---|---|
| public static final [FileDescriptor](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html) | [err](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#err) | A handle to the standard error stream. |
| public static final [FileDescriptor](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html) | [in](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#in) | A handle to the standard input stream. |
| public static final [FileDescriptor](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html) | [out](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#out) | A handle to the standard output stream. |

### Public Constructor Summary

|---|---|
|   | [FileDescriptor](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#FileDescriptor())() Constructs an (invalid) FileDescriptor object. |

### Public Method Summary

|---|---|
| void | [sync](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#sync())() Force all system buffers to synchronize with the underlying device. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| boolean | [valid](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/FileDescriptor.html#valid())() Tests if this file descriptor object is valid. |

### Inherited Method Summary

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#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

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/System.html#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

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/System.html#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

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/System.html#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](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/SyncFailedException.html) | 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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html)
**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](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#writing_toString)
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.