File

User interfaces and operating systems use system-dependent pathname strings to name files and directories. This class presents an abstract, system-independent view of hierarchical pathnames. An abstract pathname has two components:

An optional system-dependent prefix string, such as a disk-drive specifier, "/" for the UNIX root directory, or "\\\\" for a Microsoft Windows UNC pathname, and
A sequence of zero or more string names.

Each name in an abstract pathname except for the last denotes a directory; the last name may denote either a directory or a file. The empty abstract pathname has no prefix and an empty name sequence.

The conversion of a pathname string to or from an abstract pathname is inherently system-dependent. When an abstract pathname is converted into a pathname string, each name is separated from the next by a single copy of the default separator character. The default name-separator character is defined by the system property file.separator, and is made available in the public static fields separator and separatorChar of this class. When a pathname string is converted into an abstract pathname, the names within it may be separated by the default name-separator character or by any other name-separator character that is supported by the underlying system.

A pathname, whether abstract or in string form, may be either absolute or relative. An absolute pathname is complete in that no other information is required in order to locate the file that it denotes. A relative pathname, in contrast, must be interpreted in terms of information taken from some other pathname. By default the classes in the java.io package always resolve relative pathnames against the current user directory. This directory is named by the system property user.dir, and is typically the directory in which the Java virtual machine was invoked.

The prefix concept is used to handle root directories on UNIX platforms, and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms, as follows:

For UNIX platforms, the prefix of an absolute pathname is always "/". Relative pathnames have no prefix. The abstract pathname denoting the root directory has the prefix "/" and an empty name sequence.
For Microsoft Windows platforms, the prefix of a pathname that contains a drive specifier consists of the drive letter followed by ":" and possibly followed by "\\" if the pathname is absolute. The prefix of a UNC pathname is "\\\\"; the hostname and the share name are the first two names in the name sequence. A relative pathname that does not specify a drive has no prefix.

Instances of the File class are immutable; that is, once created, the abstract pathname represented by a File object will never change.

Since:: JDK1.0
See Also:: Serialized Form

Field Summary
`static String`	`pathSeparator` The system-dependent path-separator character, represented as a string for convenience.
`static char`	`pathSeparatorChar` The system-dependent path-separator character.
`static String`	`separator` The system-dependent default name-separator character, represented as a string for convenience.
`static char`	`separatorChar` The system-dependent default name-separator character.

Constructor Summary
`File (File parent, String child)` Creates a new `File` instance from a parent abstract pathname and a child pathname string.
`File (String pathname)` Creates a new `File` instance by converting the given pathname string into an abstract pathname.
`File (String parent, String child)` Creates a new `File` instance from a parent pathname string and a child pathname string.
`File (URI uri)` Creates a new `File` instance by converting the given `file:` URI into an abstract pathname.

Method Summary
`boolean`	`canRead ()` Tests whether the application can read the file denoted by this abstract pathname.
`boolean`	`canWrite ()` Tests whether the application can modify the file denoted by this abstract pathname.
`int`	`compareTo (File pathname)` Compares two abstract pathnames lexicographically.
`boolean`	`createNewFile ()` Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
`static File`	`createTempFile (String prefix, String suffix)` Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name.
`static File`	`createTempFile (String prefix, String suffix, File directory)` Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name.
`boolean`	`delete ()` Deletes the file or directory denoted by this abstract pathname.
`void`	`deleteOnExit ()` Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates.
`boolean`	`equals (Object obj)` Tests this abstract pathname for equality with the given object.
`boolean`	`exists ()` Tests whether the file or directory denoted by this abstract pathname exists.
`File`	`getAbsoluteFile ()` Returns the absolute form of this abstract pathname.
`String`	`getAbsolutePath ()` Returns the absolute pathname string of this abstract pathname.
`File`	`getCanonicalFile ()` Returns the canonical form of this abstract pathname.
`String`	`getCanonicalPath ()` Returns the canonical pathname string of this abstract pathname.
`String`	`getName ()` Returns the name of the file or directory denoted by this abstract pathname.
`String`	`getParent ()` Returns the pathname string of this abstract pathname's parent, or `null` if this pathname does not name a parent directory.
`File`	`getParentFile ()` Returns the abstract pathname of this abstract pathname's parent, or `null` if this pathname does not name a parent directory.
`String`	`getPath ()` Converts this abstract pathname into a pathname string.
`int`	`hashCode ()` Computes a hash code for this abstract pathname.
`boolean`	`isAbsolute ()` Tests whether this abstract pathname is absolute.
`boolean`	`isDirectory ()` Tests whether the file denoted by this abstract pathname is a directory.
`boolean`	`isFile ()` Tests whether the file denoted by this abstract pathname is a normal file.
`boolean`	`isHidden ()` Tests whether the file named by this abstract pathname is a hidden file.
`long`	`lastModified ()` Returns the time that the file denoted by this abstract pathname was last modified.
`long`	`length ()` Returns the length of the file denoted by this abstract pathname.
`String []`	`list ()` Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.
`String []`	`list (FilenameFilter filter)` Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`File []`	`listFiles ()` Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.
`File []`	`listFiles (FileFilter filter)` Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`File []`	`listFiles (FilenameFilter filter)` Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`static File []`	`listRoots ()` List the available filesystem roots.
`boolean`	`mkdir ()` Creates the directory named by this abstract pathname.
`boolean`	`mkdirs ()` Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.
`boolean`	`renameTo (File dest)` Renames the file denoted by this abstract pathname.
`boolean`	`setLastModified (long time)` Sets the last-modified time of the file or directory named by this abstract pathname.
`boolean`	`setReadOnly ()` Marks the file or directory named by this abstract pathname so that only read operations are allowed.
`String`	`toString ()` Returns the pathname string of this abstract pathname.
`URI`	`toURI ()` Constructs a `file:` URI that represents this abstract pathname.
`URL`	`toURL ()` Converts this abstract pathname into a `file:` URL.

Methods inherited from class java.lang.Object
`clone , finalize , getClass , notify , notifyAll , wait , wait , wait`

Field Detail

separatorChar

public static final char separatorChar

The system-dependent default name-separator character. This field is initialized to contain the first character of the value of the system property file.separator. On UNIX systems the value of this field is '/'; on Microsoft Windows systems it is '\\'.

See Also:: System.getProperty(java.lang.String)

separator

public static final String    separator

The system-dependent default name-separator character, represented as a string for convenience. This string contains a single character, namely separatorChar .

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 used to separate filenames in a sequence of files given as a path list. On UNIX systems, this character is ':'; on Microsoft Windows systems it is ';'.

See Also:: System.getProperty(java.lang.String)

pathSeparator

public static final String    pathSeparator

The system-dependent path-separator character, represented as a string for convenience. This string contains a single character, namely pathSeparatorChar .

Constructor Detail

File

public File(String    pathname)

Creates a new File instance by converting the given pathname string into an abstract pathname. If the given string is the empty string, then the result is the empty abstract pathname.

Parameters:: pathname - A pathname string
Throws:: NullPointerException - If the pathname argument is null

File

public File(String    parent,
            String    child)

Creates a new File instance from a parent pathname string and a child pathname string.

If parent is null then the new File instance is created as if by invoking the single-argument File constructor on the given child pathname string.

Otherwise the parent pathname string is taken to denote a directory, and the child pathname string is taken to denote either a directory or a file. If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way. If parent is the empty string then the new File instance is created by converting child into an abstract pathname and resolving the result against a system-dependent default directory. Otherwise each pathname string is converted into an abstract pathname and the child abstract pathname is resolved against the parent.

Parameters:: parent - The parent pathname string; child - The child pathname string
Throws:: NullPointerException - If child is null

File

public File(File    parent,
            String    child)

Creates a new File instance from a parent abstract pathname and a child pathname string.

If parent is null then the new File instance is created as if by invoking the single-argument File constructor on the given child pathname string.

Otherwise the parent abstract pathname is taken to denote a directory, and the child pathname string is taken to denote either a directory or a file. If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way. If parent is the empty abstract pathname then the new File instance is created by converting child into an abstract pathname and resolving the result against a system-dependent default directory. Otherwise each pathname string is converted into an abstract pathname and the child abstract pathname is resolved against the parent.

Parameters:: parent - The parent abstract pathname; child - The child pathname string
Throws:: NullPointerException - If child is null

File

public File(URI    uri)

Creates a new File instance by converting the given file: URI into an abstract pathname.

The exact form of a file: URI is system-dependent, hence the transformation performed by this constructor is also system-dependent.

For a given abstract pathname f it is guaranteed that

new File( f.toURI ()).equals( f.getAbsoluteFile ())

so long as the original abstract pathname, the URI, and the new abstract pathname are all created in (possibly different invocations of) the same Java virtual machine. This relationship typically does not hold, however, when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system.

Parameters:: uri - An absolute, hierarchical URI with a scheme equal to "file", a non-empty path component, and undefined authority, query, and fragment components
Throws:: NullPointerException - If uri is null; IllegalArgumentException - If the preconditions on the parameter do not hold
Since:: 1.4
See Also:: toURI() , URI

Method Detail

getName

public String    getName()

Returns the name of the file or directory denoted by this abstract pathname. This is just the last name in the pathname's name sequence. If the pathname's name sequence is empty, then the empty string is returned.

Returns:: The name of the file or directory denoted by this abstract pathname, or the empty string if this pathname's name sequence is empty

getParent

public String    getParent()

Returns the pathname string of this abstract pathname's parent, or null if this pathname does not name a parent directory.

The parent of an abstract pathname consists of the pathname's prefix, if any, and each name in the pathname's name sequence except for the last. If the name sequence is empty then the pathname does not name a parent directory.

Returns:: The pathname string of the parent directory named by this abstract pathname, or null if this pathname does not name a parent

getParentFile

public File    getParentFile()

Returns the abstract pathname of this abstract pathname's parent, or null if this pathname does not name a parent directory.

Returns:: The abstract pathname of the parent directory named by this abstract pathname, or null if this pathname does not name a parent
Since:: 1.2

getPath

public String    getPath()

Converts this abstract pathname into a pathname string. The resulting string uses the default name-separator character

definition code for java.io.File.separator

to separate the names in the name sequence.

Returns:: The string form of this abstract pathname

isAbsolute

public boolean isAbsolute()

Tests whether this abstract pathname is absolute. The definition of absolute pathname is system dependent. On UNIX systems, a pathname is absolute if its prefix is "/". On Microsoft Windows systems, a pathname is absolute if its prefix is a drive specifier followed by "\\", or if its prefix is "\\\\".

Returns:: true if this abstract pathname is absolute, false otherwise

getAbsolutePath

public String    getAbsolutePath()

Returns the absolute pathname string of this abstract pathname.

If this abstract pathname is already absolute, then the pathname string is simply returned as if by the getPath() method. If this abstract pathname is the empty abstract pathname then the pathname string of the current user directory, which is named by the system property user.dir, is returned. Otherwise this pathname is resolved in a system-dependent way. On UNIX systems, a relative pathname is made absolute by resolving it against the current user directory. On Microsoft Windows systems, a relative pathname is made absolute by resolving it against the current directory of the drive named by the pathname, if any; if not, it is resolved against the current user directory.

Returns:: The absolute pathname string denoting the same file or directory as this abstract pathname
Throws:: SecurityException - If a required system property value cannot be accessed.
See Also:: isAbsolute()

getAbsoluteFile

public File    getAbsoluteFile()

Returns the absolute form of this abstract pathname. Equivalent to new File(this.getAbsolutePath() ()).

Returns:: The absolute abstract pathname denoting the same file or directory as this abstract pathname
Throws:: SecurityException - If a required system property value cannot be accessed.
Since:: 1.2

getCanonicalPath

public String    getCanonicalPath()
                        throws IOException

Returns the canonical pathname string of this abstract pathname.

A canonical pathname is both absolute and unique. The precise definition of canonical form is system-dependent. This method first converts this pathname to absolute form if necessary, as if by invoking the getAbsolutePath() method, and then maps it to its unique form in a system-dependent way. This typically involves removing redundant names such as "." and ".." from the pathname, resolving symbolic links (on UNIX platforms), and converting drive letters to a standard case (on Microsoft Windows platforms).

Every pathname that denotes an existing file or directory has a unique canonical form. Every pathname that denotes a nonexistent file or directory also has a unique canonical form. The canonical form of the pathname of a nonexistent file or directory may be different from the canonical form of the same pathname after the file or directory is created. Similarly, the canonical form of the pathname of an existing file or directory may be different from the canonical form of the same pathname after the file or directory is deleted.

Returns:: The canonical pathname string denoting the same file or directory as this abstract pathname
Throws:: IOException - If an I/O error occurs, which is possible because the construction of the canonical pathname may require filesystem queries; SecurityException - If a required system property value cannot be accessed, or if a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file
Since:: JDK1.1

getCanonicalFile

public File    getCanonicalFile()
                      throws IOException

Returns the canonical form of this abstract pathname. Equivalent to new File(this.getCanonicalPath() ()).

Returns:: The canonical pathname string denoting the same file or directory as this abstract pathname
Throws:: IOException - If an I/O error occurs, which is possible because the construction of the canonical pathname may require filesystem queries; SecurityException - If a required system property value cannot be accessed, or if a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file
Since:: 1.2

toURL

public URL

java.io Class File

separatorChar

separator

pathSeparatorChar

pathSeparator

File

File

File

File

getName

getParent

getParentFile

getPath

isAbsolute

getAbsolutePath

getAbsoluteFile

getCanonicalPath

getCanonicalFile

toURL

java.io
Class File