Class java.io.File - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.io.File

java.lang.Object
   |
   +----java.io.File

public class File
extends Object
implements Serializable

Instances of this class represent the name of a file or directory on the host file system. A file is specified by a pathname, which can either be an absolute pathname or a pathname relative to the current working directory. The pathname must follow the naming conventions of the host platform.

The File class is intended to provide an abstraction that deals with most of the machine dependent complexities of files and pathnames in a machine-independent fashion.

Note that whenever a filename or path is used it is assumed that the host's file naming conventions are used.

pathSeparator: The system-dependent path separator string.
pathSeparatorChar: The system-dependent path separator character.
separator: The system-dependent path separator string.
separatorChar: The system-dependent path separator character.

File(File, String): Creates a File instance that represents the file with the specified name in the specified directory.
File(String): Creates a File instance that represents the file whose pathname is the given path argument.
File(String, String): Creates a File instance whose pathname is the pathname of the specified directory, followed by the separator character, followed by the name argument.

canRead(): Tests if the application can read from the specified file.
canWrite(): Tests if the application can write to this file.
delete(): Deletes the file specified by this object.
equals(Object): Compares this object against the specified object.
exists(): Tests if this File exists.
getAbsolutePath(): Returns the absolute pathname of the file represented by this object.
getCanonicalPath(): Returns the canonical form of this File object's pathname.
getName(): Returns the name of the file represented by this object.
getParent(): Returns the parent part of the pathname of this File object, or null if the name has no parent part.
getPath(): Returns the pathname of the file represented by this object.
hashCode(): Computes a hashcode for the file.
isAbsolute(): Tests if the file represented by this File object is an absolute pathname.
isDirectory(): Tests if the file represented by this File object is a directory.
isFile(): Tests if the file represented by this File object is a "normal" file.
lastModified(): Returns the time that the file represented by this File object was last modified.
length(): Returns the length of the file represented by this File object.
list(): Returns a list of the files in the directory specified by this File object.
list(FilenameFilter): Returns a list of the files in the directory specified by this File that satisfy the specified filter.
mkdir(): Creates a directory whose pathname is specified by this File object.
mkdirs(): Creates a directory whose pathname is specified by this File object, including any necessary parent directories.
renameTo(File): Renames the file specified by this File object to have the pathname given by the File argument.
toString(): Returns a string representation of this object.

separator

 public static final String separator

The system-dependent path separator string. This field is initialized to contain the value of the system property file.separator.

See Also:: getProperty

separatorChar

 public static final char separatorChar

The system-dependent path separator character. This field is initialized to contain the first character of the value of the system property file.separator. This character separates the directory and file components in a filename.

See Also:: getProperty

pathSeparator

 public static final String pathSeparator

The system-dependent path separator string. This field is initialized to contain the value of the system property path.separator.

See Also:: getProperty

pathSeparatorChar

 public static final char pathSeparatorChar

The system-dependent path separator character. This field is initialized to contain the first character of the value of the system property path.separator. This character is often used to separate filenames in a sequence of files given as a "path list".

See Also:: getProperty

File

 public File(String path)

Creates a File instance that represents the file whose pathname is the given path argument.

Parameters:: path - the file pathname.
Throws: NullPointerException: if the file path is equal to null.
See Also:: getPath

File

 public File(String path,
             String name)

Creates a File instance whose pathname is the pathname of the specified directory, followed by the separator character, followed by the name argument.

Parameters:: path - the directory pathname.; name - the file pathname.
See Also:: getPath, separator

File

 public File(File dir,
             String name)

Creates a File instance that represents the file with the specified name in the specified directory.

If the directory argument is null, the resulting File instance represents a file in the (system-dependent) current directory whose pathname is the name argument. Otherwise, the File instance represents a file whose pathname is the pathname of the directory, followed by the separator character, followed by the name argument.

Parameters:: dir - the directory.; name - the file pathname.
See Also:: getPath, separator

getName

 public String getName()

Returns the name of the file represented by this object. The name is everything in the pathame after the last occurrence of the separator character.

Returns:: the name of the file (without any directory components) represented by this File object.
See Also:: getPath, separator

getPath

 public String getPath()

Returns the pathname of the file represented by this object.

Returns:: the pathname represented by this File object.

getAbsolutePath

 public String getAbsolutePath()

Returns the absolute pathname of the file represented by this object. If this object represents an absolute pathname, then return the pathname. Otherwise, return a pathname that is a concatenation of the current user directory, the separator character, and the pathname of this file object.

The system property user.dir contains the current user directory.

Returns:: a system-dependent absolute pathname for this File.
See Also:: getPath, isAbsolute, getProperty

getCanonicalPath

 public String getCanonicalPath() throws IOException

Returns the canonical form of this File object's pathname. The precise definition of canonical form is system-dependent, but it usually specifies an absolute pathname in which all relative references and references to the current user directory have been completely resolved. The canonical form of a pathname of a nonexistent file may not be defined.

Throws: IOException: If an I/O error occurs, which is possible because the construction of the canonical path may require filesystem queries.

getParent

 public String getParent()

Returns the parent part of the pathname of this File object, or null if the name has no parent part. The parent part is generally everything leading up to the last occurrence of the separator character, although the precise definition is system dependent. On UNIX, for example, the parent part of "/usr/lib" is "/usr", whose parent part is "/", which in turn has no parent. On Windows platforms, the parent part of "c:\java" is "c:\", which in turn has no parent.

See Also:: getPath, getCanonicalPath, separator

exists

 public boolean exists()

Tests if this File exists.

Returns:: true if the file specified by this object exists; false otherwise.
Throws: SecurityException: if a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

canWrite

 public boolean canWrite()

Tests if the application can write to this file.

Returns:: true if the application is allowed to write to a file whose name is specified by this object; false otherwise.
Throws: SecurityException: if a security manager exists, its checkWrite method is called with the pathname of this File to see if the application is allowed write access to the file.
See Also:: getPath, checkWrite

canRead

 public boolean canRead()

Tests if the application can read from the specified file.

Returns:: true if the file specified by this object exists and the application can read the file; false otherwise.
Throws: SecurityException: if a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

isFile

 public boolean isFile()

Tests if the file represented by this File object is a "normal" file.

A file is "normal" if it is not a directory and, in addition, satisfies other system-dependent criteria. Any non-directory file created by a Java application is guaranteed to be a normal file.

Returns:: true if the file specified by this object exists and is a "normal" file; false otherwise.
Throws: SecurityException: If a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

isDirectory

 public boolean isDirectory()

Tests if the file represented by this File object is a directory.

Returns:: true if this File exists and is a directory; false otherwise.
Throws: SecurityException: if a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

isAbsolute

 public native boolean isAbsolute()

Tests if the file represented by this File object is an absolute pathname. The definition of an absolute pathname is system dependent. For example, on UNIX, a pathname is absolute if its first character is the separator character. On Windows platforms, a pathname is absolute if its first character is an ASCII '\' or '/', or if it begins with a letter followed by a colon.

Returns:: true if the pathname indicated by the File object is an absolute pathname; false otherwise.
See Also:: getPath, separator

lastModified

 public long lastModified()

Returns the time that the file represented by this File object was last modified.

The return value is system dependent and should only be used to compare with other values returned by last modified. It should not be interpreted as an absolute time.

Returns:: the time the file specified by this object was last modified, or 0L if the specified file does not exist.
Throws: SecurityException: if a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

length

 public long length()

Returns the length of the file represented by this File object.

Returns:: the length, in bytes, of the file specified by this object, or 0L if the specified file does not exist.
Throws: SecurityException: if a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

mkdir

 public boolean mkdir()

Creates a directory whose pathname is specified by this File object.

Returns:: true if the directory could be created; false otherwise.
Throws: SecurityException: if a security manager exists, its checkWrite method is called with the pathname of this File to see if the application is allowed write access to the file.
See Also:: getPath, checkWrite

renameTo

 public boolean renameTo(File dest)

Renames the file specified by this File object to have the pathname given by the File argument.

Parameters:: dest - the new filename.
Returns:: true if the renaming succeeds; false otherwise.
Throws: SecurityException: if a security manager exists, its checkWrite method is called both with the pathname of this file object and with the pathname of the destination target object to see if the application is allowed to write to both files.
See Also:: getPath, checkWrite

mkdirs

 public boolean mkdirs()

Creates a directory whose pathname is specified by this File object, including any necessary parent directories.

Returns:: true if the directory (or directories) could be created; false otherwise.
Throws: SecurityException: if a security manager exists, its checkWrite method is called with the pathname of each of the directories that is to be created, before any of the directories are created.
See Also:: getPath, checkWrite

list

 public String[] list()

Returns a list of the files in the directory specified by this File object.

Returns:: an array of file names in the specified directory. This list does not include the current directory or the parent directory ("." and ".." on Unix systems).
Throws: SecurityException: If a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, checkRead

list

 public String[] list(FilenameFilter filter)

Returns a list of the files in the directory specified by this File that satisfy the specified filter.

Parameters:: filter - a filename filter.
Returns:: an array of file names in the specified directory. This list does not include the current directory or the parent directory ("." and ".." on Unix systems).
Throws: SecurityException: If a security manager exists, its checkRead method is called with the pathname of this File to see if the application is allowed read access to the file.
See Also:: getPath, FilenameFilter, checkRead

delete

 public boolean delete()

Deletes the file specified by this object. If the target file to be deleted is a directory, it must be empty for deletion to succeed.

Returns:: true if the file is successfully deleted; false otherwise.
Throws: SecurityException: if a security manager exists, its checkDelete method is called with the pathname of this File to see if the application is allowed to delete the file.
See Also:: getPath, checkDelete

hashCode

 public int hashCode()

Computes a hashcode for the file.

Returns:: a hash code value for this File object.
Overrides:: hashCode in class Object

equals

 public boolean equals(Object obj)

Compares this object against the specified object. Returns true if and only if the argument is not null and is a File object whose pathname is equal to the pathname of this object.

Parameters:: obj - the object to compare with.
Returns:: true if the objects are the same; false otherwise.
Overrides:: equals in class Object

toString

 public String toString()

Returns a string representation of this object.

Returns:: a string giving the pathname of this object.
Overrides:: toString in class Object
See Also:: getPath

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