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, 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.

从以下版本开始:

JDK1.0

另请参阅:

FileInputStream, FileOutputStream

字段概要

字段
限定符和类型	字段	说明
`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.

构造器概要

构造器
构造器说明

FileDescriptor()
Constructs an (invalid) FileDescriptor object.

构造器
构造器	说明
`FileDescriptor()`	Constructs an (invalid) FileDescriptor object.

方法概要

所有方法实例方法具体方法
限定符和类型	方法	说明
`void`	`sync()`	Force all system buffers to synchronize with the underlying device.
`boolean`	`valid()`	Tests if this file descriptor object is valid.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - err
```
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.
    
    另请参阅:
    
    System.err
  - in
```
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.
    
    另请参阅:
    
    System.in
  - out
```
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.
    
    另请参阅:
    
    System.out
- 构造器详细资料
  - FileDescriptor
```
public FileDescriptor()
```
    Constructs an (invalid) FileDescriptor object.
- 方法详细资料
  - valid
```
public boolean valid()
```
    Tests if this file descriptor object is valid.
    
    返回:
    
    true if the file descriptor object represents a valid, open file, socket, or other active I/O connection; 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 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.
    
    抛出:
    
    SyncFailedException - Thrown when the buffers cannot be flushed, or because the system cannot guarantee that all the buffers have been synchronized with physical media.
    
    从以下版本开始:
    
    JDK1.1

类 FileDescriptor

字段概要

构造器概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

err

in

out

构造器详细资料

FileDescriptor

方法详细资料

valid

sync