Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class File - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.io
Class File

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

public class File
extends Object
implements Serializable, Comparable

An abstract representation of file and directory pathnames.

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 Win32 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 Win32 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 Win32 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.

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 to the file denoted by this abstract pathname.

int compareTo(File pathname)
          Compares two abstract pathnames lexicographically.

int compareTo(Object o)
          Compares this abstract pathname to another object.

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 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.

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 Win32 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 Win32 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

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:: JDK1.2

getPath

public String getPath()

Converts this abstract pathname into a pathname string. The resulting string uses the default name-separator character 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 Win32 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 Win32 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
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
Since:: JDK1.2

getCanonicalPath

public String getCanonicalPath()
                        throws IOException

Returns the canonical pathname string of this abstract pathname.

The precise definition of canonical form is system-dependent, but canonical forms are always absolute. Thus if this abstract pathname is relative it will be converted to absolute form as if by the getAbsoluteFile() method.

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
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
Since:: JDK1.2

toURL

public URL toURL()
          throws MalformedURLException

Converts this abstract pathname into a file: URL. The exact form of the URL is system-dependent. If it can be determined that the file denoted by this abstract pathname is a directory, then the resulting URL will end with a slash.

Since:: JDK1.2
See Also:: URL

canRead

public boolean canRead()

Tests whether the application can read the file denoted by this abstract pathname.

Returns:: true if and only if the file specified by this abstract pathname exists and can be read by the application; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

canWrite

public boolean canWrite()

Tests whether the application can modify to the file denoted by this abstract pathname.

Returns:: true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method denies write access to the file

exists

public boolean exists()

Tests whether the file denoted by this abstract pathname exists.

Returns:: true if and only if the file denoted by this abstract pathname exists; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

isDirectory

public boolean isDirectory()

Tests whether the file denoted by this abstract pathname is a directory.

Returns:: true if and only if the file denoted by this abstract pathname exists and is a directory; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

isFile

public boolean isFile()

Tests whether the file denoted by this abstract pathname 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 and only if the file denoted by this abstract pathname exists and is a normal file; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

isHidden

public boolean isHidden()

Tests whether the file named by this abstract pathname is a hidden file. The exact definition of hidden is system-dependent. On UNIX systems, a file is considered to be hidden if its name begins with a period character ('.'). On Win32 systems, a file is considered to be hidden if it has been marked as such in the filesystem.

Returns:: true if and only if the file denoted by this abstract pathname is hidden according to the conventions of the underlying platform
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file
Since:: JDK1.2

lastModified

public long lastModified()

Returns the time that the file denoted by this abstract pathname was last modified.

Returns:: A long value representing the time the file was last modified, measured in milliseconds since the epoch (00:00:00 GMT, January 1, 1970), or 0L if the file does not exist or if an I/O error occurs
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

length

public long length()

Returns the length of the file denoted by this abstract pathname.

Returns:: The length, in bytes, of the file denoted by this abstract pathname, or 0L if the file does not exist
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

createNewFile

public boolean createNewFile()
                      throws IOException

Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. The check for the existence of the file and the creation of the file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the file. This method, in combination with the deleteOnExit() method, can therefore serve as the basis for a simple but reliable cooperative file-locking protocol.

Returns:: true if the named file does not exist and was successfully created; false if the named file already exists
Throws:: IOException - If an I/O error occurred; SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method denies write access to the file
Since:: JDK1.2

delete

public boolean delete()

Deletes the file or directory denoted by this abstract pathname. If this pathname denotes a directory, then the directory must be empty in order to be deleted.

Returns:: true if and only if the file or directory is successfully deleted; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkDelete(java.lang.String) method denies delete access to the file

deleteOnExit

public void deleteOnExit()

Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates. Deletion will be attempted only for normal termination of the virtual machine, as defined by the Java Language Specification (12.9).

Once deletion has been requested, it is not possible to cancel the request. This method should therefore be used with care.

Throws:: SecurityException - If a security manager exists and its SecurityManager.checkDelete(java.lang.String) method denies delete access to the file
Since:: JDK1.2
See Also:: delete()

list

public String[] list()

Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.

If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of strings is returned, one for each file or directory in the directory. Names denoting the directory itself and the directory's parent directory are not included in the result. Each string is a file name rather than a complete path.

There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.

Returns:: An array of strings naming the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the directory

list

public 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. The behavior of this method is the same as that of the list() method, except that the strings in the returned array must satisfy the filter. If the given filter is null then all names are accepted. Otherwise, a name satisfies the filter if and only if the value true results when the FilenameFilter.accept(java.io.File, java.lang.String) method of the filter is invoked on this abstract pathname and the name of a file or directory in the directory that it denotes.

Parameters:: filter - A filename filter
Returns:: An array of strings naming the files and directories in the directory denoted by this abstract pathname that were accepted by the given filter. The array will be empty if the directory is empty or if no names were accepted by the filter. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the directory

listFiles

public File[] listFiles()

Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.

If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of File objects is returned, one for each file or directory in the directory. Pathnames denoting the directory itself and the directory's parent directory are not included in the result. Each resulting abstract pathname is constructed from this abstract pathname using the File(File, String) constructor. Therefore if this pathname is absolute then each resulting pathname is absolute; if this pathname is relative then each resulting pathname will be relative to the same directory.

There is no guarantee that the name strings in the resulting array will appear in any specific order; they are not, in particular, guaranteed to appear in alphabetical order.

Returns:: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the directory
Since:: JDK1.2

listFiles

public 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. The behavior of this method is the same as that of the listFiles() method, except that the pathnames in the returned array must satisfy the filter. If the given filter is null then all pathnames are accepted. Otherwise, a pathname satisfies the filter if and only if the value true results when the FilenameFilter.accept(java.io.File, java.lang.String) method of the filter is invoked on this abstract pathname and the name of a file or directory in the directory that it denotes.

Parameters:: filter - A filename filter
Returns:: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the directory
Since:: JDK1.2

listFiles

public File[] listFiles(FileFilter filter)

Parameters:: filter - A filename filter
Returns:: An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the directory
Since:: JDK1.2

mkdir

public boolean mkdir()

Creates the directory named by this abstract pathname.

Returns:: true if and only if the directory was created; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method does not permit the named directory to be created

mkdirs

public boolean mkdirs()

Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories. Note that if this operation fails it may have succeeded in creating some of the necessary parent directories.

Returns:: true if and only if the directory was created, along with all necessary parent directories; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method does not permit the named directory and all necessary parent directories and to be created

renameTo

public boolean renameTo(File dest)

Renames the file denoted by this abstract pathname.

Parameters:: dest - The new abstract pathname for the named file
Returns:: true if and only if the renaming succeeded; false otherwise
Throws:: SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method denies write access to both the old and new pathnames; NullPointerException - If parameter dest is null

setLastModified

public boolean setLastModified(long time)

Sets the last-modified time of the file or directory named by this abstract pathname.

All platforms support file-modification times to the nearest second, but some provide more precision. The argument will be truncated to fit the supported precision. If the operation succeeds and no intervening operations on the file take place, then the next invocation of the lastModified() method will return the (possibly truncated) time argument that was passed to this method.

Parameters:: time - The new last-modified time, measured in milliseconds since the epoch (00:00:00 GMT, January 1, 1970)
Throws:: IllegalArgumentException - If the argument is negative; SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method denies write access to the named file
Since:: JDK1.2

setReadOnly

public boolean setReadOnly()

Marks the file or directory named by this abstract pathname so that only read operations are allowed. After invoking this method the file or directory is guaranteed not to change until it is either deleted or marked to allow write access. Whether or not a read-only file or directory may be deleted depends upon the underlying system.

Throws:: SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method denies write access to the named file
Since:: JDK1.2

listRoots

public static File[] listRoots()

List the available filesystem roots.

A particular Java platform may support zero or more hierarchically-organized file systems. Each file system has a root directory from which all other files in that file system can be reached. Windows platforms, for example, have a root directory for each active drive; UNIX platforms have a single root directory, namely "/". The set of available filesystem roots is affected by various system-level operations such the insertion or ejection of removable media and the disconnecting or unmounting of physical or virtual disk drives.

This method returns an array of File objects that denote the root directories of the available filesystem roots. It is guaranteed that the canonical pathname of any file physically present on the local machine will begin with one of the roots returned by this method.

The canonical pathname of a file that resides on some other machine and is accessed via a remote-filesystem protocol such as SMB or NFS may or may not begin with one of the roots returned by this method. If the pathname of a remote file is syntactically indistinguishable from the pathname of a local file then it will begin with one of the roots returned by this method. Thus, for example, File objects denoting the root directories of the mapped network drives of a Windows platform will be returned by this method, while File objects containing UNC pathnames will not be returned by this method.

Unlike most methods in this class, this method does not throw security exceptions. If a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to a particular root directory, then that directory will not appear in the result.

Returns:: An array of File objects denoting the available filesystem roots, or null if the set of roots could not be determined. The array will be empty if there are no filesystem roots.
Since:: JDK1.2

createTempFile

public static File createTempFile(String prefix,
                                  String suffix,
                                  File directory)
                           throws IOException

Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name. If this method returns successfully then it is guaranteed that:

The file denoted by the returned abstract pathname did not exist before this method was invoked, and
Neither this method nor any of its variants will return the same abstract pathname again in the current invocation of the virtual machine.

This method provides only part of a temporary-file facility. To arrange for a file created by this method to be deleted automatically, use the deleteOnExit() method.

The prefix argument must be at least three characters long. It is recommended that the prefix be a short, meaningful string such as "hjb" or "mail". The suffix argument may be null, in which case the suffix ".tmp" will be used.

To create the new file, the prefix and the suffix may first be adjusted to fit the limitations of the underlying platform. If the prefix is too long then it will be truncated, but its first three characters will always be preserved. If the suffix is too long then it too will be truncated, but if it begins with a period character ('.') then the period and the first three characters following it will always be preserved. Once these adjustments have been made the name of the new file will be generated by concatenating the prefix, five or more internally-generated characters, and the suffix.

If the directory argument is null then the system-dependent default temporary-file directory will be used. The default temporary-file directory is specified by the system property java.io.tmpdir. On UNIX systems the default value of this property is typically "/tmp" or "/var/tmp"; on Win32 systems it is typically "c:\\temp".

Parameters:: prefix - The prefix string to be used in generating the file's name; must be at least three characters long; suffix - The suffix string to be used in generating the file's name; may be null, in which case the suffix ".tmp" will be used; directory - The directory in which the file is to be created, or null if the default temporary-file directory is to be used
Returns:: An abstract pathname denoting a newly-created empty file
Throws:: IllegalArgumentException - If the prefix argument contains fewer than three characters; IOException - If a file could not be created; SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method does not allow a file to be created
Since:: JDK1.2

createTempFile

public static File createTempFile(String prefix,
                                  String suffix)
                           throws IOException

Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name. Invoking this method is equivalent to invoking createTempFile(prefix, suffix, null).

Parameters:: prefix - The prefix string to be used in generating the file's name; must be at least three characters long; suffix - The suffix string to be used in generating the file's name; may be null, in which case the suffix ".tmp" will be used
Returns:: An abstract pathname denoting a newly-created empty file
Throws:: IllegalArgumentException - If the prefix argument contains fewer than three characters; IOException - If a file could not be created; SecurityException - If a security manager exists and its SecurityManager.checkWrite(java.io.FileDescriptor) method does not allow a file to be created
Since:: JDK1.2

compareTo

public int compareTo(File pathname)

Compares two abstract pathnames lexicographically. The ordering defined by this method depends upon the underlying system. On UNIX systems, alphabetic case is significant in comparing pathnames; on Win32 systems it is not.

Parameters:: pathname - The abstract pathname to be compared to this abstract pathname
Returns:: Zero if the argument is equal to this abstract pathname, a value less than zero if this abstract pathname is lexicographically less than the argument, or a value greater than zero if this abstract pathname is lexicographically greater than the argument
Since:: JDK1.2

compareTo

public int compareTo(Object o)

Compares this abstract pathname to another object. If the other object is an abstract pathname, then this function behaves like compareTo(File). Otherwise, it throws a ClassCastException, since abstract pathnames can only be compared to abstract pathnames.

Specified by:: compareTo in interface Comparable

Parameters:: o - The Object to be compared to this abstract pathname
Returns:: If the argument is an abstract pathname, returns zero if the argument is equal to this abstract pathname, a value less than zero if this abstract pathname is lexicographically less than the argument, or a value greater than zero if this abstract pathname is lexicographically greater than the argument
Throws:: ClassCastException - if the argument is not an abstract pathname
Since:: JDK1.2
See Also:: Comparable

equals

public boolean equals(Object obj)

Tests this abstract pathname for equality with the given object. Returns true if and only if the argument is not null and is an abstract pathname that denotes the same file or directory as this abstract pathname. Whether or not two abstract pathnames are equal depends upon the underlying system. On UNIX systems, alphabetic case is significant in comparing pathnames; on Win32 systems it is not.

Overrides:: equals in class Object

Parameters:: obj - The object to be compared with this abstract pathname
Returns:: true if and only if the objects are the same; false otherwise

hashCode

public int hashCode()

Computes a hash code for this abstract pathname. Because equality of abstract pathnames is inherently system-dependent, so is the computation of their hash codes. On UNIX systems, the hash code of an abstract pathname is equal to the exclusive or of its pathname string and the decimal value 1234321. On Win32 systems, the hash code is equal to the exclusive or of its pathname string, convered to lower case, and the decimal value 1234321.

Overrides:: hashCode in class Object

Returns:: A hash code for this abstract pathname

toString

public String toString()

Returns the pathname string of this abstract pathname. This is just the string returned by the getPath() method.

Overrides:: toString in class Object

Returns:: The string form of this abstract pathname

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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.

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 to the file denoted by this abstract pathname.
`int`	`compareTo(File pathname)` Compares two abstract pathnames lexicographically.
`int`	`compareTo(Object o)` Compares this abstract pathname to another object.
`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 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.
`URL`	`toURL()` Converts this abstract pathname into a `file:` URL.

Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class File - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

java.io Class File

separatorChar

separator

pathSeparatorChar

pathSeparator

File

File

File

getName

getParent

getParentFile

getPath

isAbsolute

getAbsolutePath

getAbsoluteFile

getCanonicalPath

getCanonicalFile

toURL

canRead

canWrite

exists

isDirectory

isFile

isHidden

lastModified

length

createNewFile

delete

deleteOnExit

list

list

listFiles

listFiles

listFiles

mkdir

mkdirs

renameTo

setLastModified

setReadOnly

listRoots

createTempFile

createTempFile

compareTo

compareTo

equals

hashCode

toString

java.io
Class File