java.io

Class File

java.lang.Object

java.io.File

All Implemented Interfaces:

Serializable, Comparable<File>

public class File
extends Object
implements Serializable, Comparable<File>

This class represents a file or directory on a local disk. It provides facilities for dealing with a variety of systems that use various types of path separators ("/" versus "\", for example). It also contains method useful for creating and deleting files and directories.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	pathSeparator This is the string that is used to separate the host name from the path name in paths that include the host name.
static char	pathSeparatorChar This is the first character of the string used to separate the host name from the path name in paths that include a host.
static String	separator This is the path separator string for the current host.
static char	separatorChar This is the first character of the file separator string.

Constructor Summary

Constructors

Constructor and Description
File(File directory, String name) This method initializes a new File object to represent a file in the specified directory.
File(String name) This method initializes a new File object to represent a file with the specified path.
File(String dirPath, String name) This method initializes a new File object to represent a file in the specified named directory.
File(URI uri) This method initializes a new File object to represent a file corresponding to the specified file: protocol URI.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	canExecute() This method tests whether or not the current thread is allowed to to execute the file pointed to by this object.
boolean	canRead() This method tests whether or not the current thread is allowed to to read the file pointed to by this object.
boolean	canWrite() This method test whether or not the current thread is allowed to write to this object.
int	compareTo(File other) This method compares the specified File to this one to test for equality.
boolean	createNewFile() This method creates a new file of zero length with the same name as the path of this File object if an only if that file does not already exist.
static File	createTempFile(String prefix, String suffix) This method creates a temporary file in the system temporary directory.
static File	createTempFile(String prefix, String suffix, File directory) This method creates a temporary file in the specified directory.
boolean	delete() This method deletes the file represented by this object.
void	deleteOnExit() Calling this method requests that the file represented by this object be deleted when the virtual machine exits.
boolean	equals(Object obj) This method tests two File objects for equality by comparing the path of the specified File against the path of this object.
boolean	exists() This method tests whether or not the file represented by the object actually exists on the filesystem.
File	getAbsoluteFile() This method returns a File object representing the absolute path of this object.
String	getAbsolutePath() This method returns the path of this file as an absolute path name.
File	getCanonicalFile() This method returns a File object representing the canonical path of this object.
String	getCanonicalPath() This method returns a canonical representation of the pathname of this file.
String	getName() This method returns the name of the file.
String	getParent() This method returns a String the represents this file's parent.
File	getParentFile() This method returns a File object representing the parent file of this one.
String	getPath() Returns the path name that represents this file.
int	hashCode() This method returns a hash code representing this file.
boolean	isAbsolute() This method returns true if this object represents an absolute file path and false if it does not.
boolean	isDirectory() This method tests whether or not the file represented by this object is a directory.
boolean	isFile() This method tests whether or not the file represented by this object is a "plain" file.
boolean	isHidden() This method tests whether or not this file represents a "hidden" file.
long	lastModified() This method returns the last modification time of this file.
long	length() This method returns the length of the file represented by this object, or 0 if the specified file does not exist.
String[]	list() This method returns a array of String's representing the list of files is then directory represented by this object.
String[]	list(FilenameFilter filter) This method returns a array of String's representing the list of files is then directory represented by this object.
File[]	listFiles() This method returns an array of File objects representing all the files in the directory represented by this object.
File[]	listFiles(FileFilter filter) This method returns an array of File objects representing all the files in the directory represented by this object.
File[]	listFiles(FilenameFilter filter) This method returns an array of File objects representing all the files in the directory represented by this object.
static File[]	listRoots() This method returns an array of filesystem roots.
boolean	mkdir() This method creates a directory for the path represented by this object.
boolean	mkdirs() This method creates a directory for the path represented by this file.
boolean	renameTo(File dest) This method renames the file represented by this object to the path of the file represented by the argument File.
boolean	setExecutable(boolean executable) This method sets the owner's execute permission for the File represented by this object.
boolean	setExecutable(boolean executable, boolean ownerOnly) This method sets the execute permissions for the File represented by this object.
boolean	setLastModified(long time) This method sets the modification time on the file to the specified value.
boolean	setReadable(boolean readable) This method sets the owner's read permission for the File represented by this object.
boolean	setReadable(boolean readable, boolean ownerOnly) This method sets the read permissions for the File represented by this object.
boolean	setReadOnly() This method sets the file represented by this object to be read only.
boolean	setWritable(boolean writable) This method sets the owner's write permission for the File represented by this object.
boolean	setWritable(boolean writable, boolean ownerOnly) This method sets the write permissions for the File represented by this object.
String	toString() This method returns a String that is the path name of the file as returned by getPath.
URI	toURI()
URL	toURL() This method returns a URL with the file: protocol that represents this file.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

separator

public static final String separator

This is the path separator string for the current host. This field contains the value of the file.separator system property. An example separator string would be "/" on the GNU system.

separatorChar

public static final char separatorChar

This is the first character of the file separator string. On many hosts (for example, on the GNU system), this represents the entire separator string. The complete separator string is obtained from the file.separatorsystem property.

pathSeparator

public static final String pathSeparator

This is the string that is used to separate the host name from the path name in paths that include the host name. It is the value of the path.separator system property.

pathSeparatorChar

public static final char pathSeparatorChar

This is the first character of the string used to separate the host name from the path name in paths that include a host. The separator string is taken from the path.separator system property.

Constructor Detail

File

public File(String name)

This method initializes a new File object to represent a file with the specified path.

Parameters:

name - The path name of the file

File

public File(String dirPath,
    String name)

This method initializes a new File object to represent a file in the specified named directory. The path name to the file will be the directory name plus the separator string plus the file name. If the directory path name ends in the separator string, another separator string will still be appended.

Parameters:

dirPath - The path to the directory the file resides in

name - The name of the file

File

public File(File directory,
    String name)

This method initializes a new File object to represent a file in the specified directory. If the directory argument is null, the file is assumed to be in the current directory as specified by the user.dir system property

Parameters:

directory - The directory this file resides in

name - The name of the file

File

public File(URI uri)

This method initializes a new File object to represent a file corresponding to the specified file: protocol URI.

Parameters:

uri - The URI

Throws:

IllegalArgumentException - if the URI is not hierarchical

Method Detail

canRead

public boolean canRead()

This method tests whether or not the current thread is allowed to to read the file pointed to by this object. This will be true if and and only if 1) the file exists and 2) the SecurityManager (if any) allows access to the file via it's checkRead method 3) the file is readable.

Returns:

true if reading is allowed, false otherwise

Throws:

SecurityException - If the SecurityManager does not allow access to the file

canWrite

public boolean canWrite()

This method test whether or not the current thread is allowed to write to this object. This will be true if and only if 1) The SecurityManager (if any) allows write access to the file and 2) The file exists and 3) The file is writable. To determine whether or not a non-existent file can be created, check the parent directory for write access.

Returns:

true if writing is allowed, false otherwise

Throws:

SecurityException - If the SecurityManager does not allow access to the file

canExecute

public boolean canExecute()

This method tests whether or not the current thread is allowed to to execute the file pointed to by this object. This will be true if and and only if 1) the file exists and 2) the SecurityManager (if any) allows access to the file via it's checkExec method 3) the file is executable.

Returns:

true if execution is allowed, false otherwise

Throws:

SecurityException - If the SecurityManager does not allow access to the file

createNewFile

public boolean createNewFile()
                      throws IOException

This method creates a new file of zero length with the same name as the path of this File object if an only if that file does not already exist.

A SecurityManager.checkWrite check is done prior to performing this action.

Returns:

true if the file was created, false if the file alread existed.

Throws:

IOException - If an I/O error occurs

SecurityException - If the SecurityManager will not allow this operation to be performed.

Since:

1.2

delete

public boolean delete()

This method deletes the file represented by this object. If this file is a directory, it must be empty in order for the delete to succeed.

Returns:

true if the file was deleted, false otherwise

Throws:

SecurityException - If deleting of the file is not allowed

equals

public boolean equals(Object obj)

This method tests two File objects for equality by comparing the path of the specified File against the path of this object. The two objects are equal if an only if 1) The argument is not null 2) The argument is a File object and 3) The path of the Fileargument is equal to the path of this object.

The paths of the files are determined by calling the getPath() method on each object.

Overrides:

equals in class Object

Parameters:

obj - the Object to compare to

Returns:

true if the two objects are equal, false otherwise.

See Also:

Object.hashCode()

exists

public boolean exists()

This method tests whether or not the file represented by the object actually exists on the filesystem.

Returns:

true if the file exists, falseotherwise.

Throws:

SecurityException - If reading of the file is not permitted

getAbsolutePath

public String getAbsolutePath()

This method returns the path of this file as an absolute path name. If the path name is already absolute, then it is returned. Otherwise the value returned is the current directory plus the separatory string plus the path of the file. The current directory is determined from the user.dir system property.

Returns:

The absolute path of this file

getAbsoluteFile

public File getAbsoluteFile()

This method returns a File object representing the absolute path of this object.

Returns:

A File with the absolute path of the object.

Since:

1.2

getCanonicalPath

public String getCanonicalPath()
                        throws IOException

This method returns a canonical representation of the pathname of this file. The actual form of the canonical representation is system-dependent. On the GNU system, conversion to canonical form involves the removal of redundant separators, references to "." and "..", and symbolic links.

Note that this method, unlike the other methods which return path names, can throw an IOException. This is because native method might be required in order to resolve the canonical path

Throws:

IOException - If an error occurs

getCanonicalFile

public File getCanonicalFile()
                      throws IOException

This method returns a File object representing the canonical path of this object.

Returns:

A File instance representing the canonical path of this object.

Throws:

IOException - If an error occurs.

Since:

1.2

getName

public String getName()

This method returns the name of the file. This is everything in the complete path of the file after the last instance of the separator string.

Returns:

The file name

getParent

public String getParent()

This method returns a String the represents this file's parent. null is returned if the file has no parent. The parent is determined via a simple operation which removes the name after the last file separator character, as determined by the platform.

Returns:

The parent directory of this file

getParentFile

public File getParentFile()

This method returns a File object representing the parent file of this one.

Returns:

a File for the parent of this object. null will be returned if this object does not have a parent.

Since:

1.2

getPath

public String getPath()

Returns the path name that represents this file. May be a relative or an absolute path name

Returns:

The pathname of this file

hashCode

public int hashCode()

This method returns a hash code representing this file. It is the hash code of the path of this file (as returned by getPath()) exclusived or-ed with the value 1234321.

Overrides:

hashCode in class Object

Returns:

The hash code for this object

See Also:

Object.equals(Object), System.identityHashCode(Object)

isAbsolute

public boolean isAbsolute()

This method returns true if this object represents an absolute file path and false if it does not. The definition of an absolute path varies by system. As an example, on GNU systems, a path is absolute if it starts with a "/".

Returns:

true if this object represents an absolute file name, false otherwise.

isDirectory

public boolean isDirectory()

This method tests whether or not the file represented by this object is a directory. In order for this method to return true, the file represented by this object must exist and be a directory.

Returns:

true if this file is a directory, false otherwise

Throws:

SecurityException - If reading of the file is not permitted

isFile

public boolean isFile()

This method tests whether or not the file represented by this object is a "plain" file. A file is a plain file if and only if it 1) Exists, 2) Is not a directory or other type of special file.

Returns:

true if this is a plain file, false otherwise

Throws:

SecurityException - If reading of the file is not permitted

isHidden

public boolean isHidden()

This method tests whether or not this file represents a "hidden" file. On GNU systems, a file is hidden if its name begins with a "." character. Files with these names are traditionally not shown with directory listing tools.

Returns:

true if the file is hidden, false otherwise.

Since:

1.2

lastModified

public long lastModified()

This method returns the last modification time of this file. The time value returned is an abstract value that should not be interpreted as a specified time value. It is only useful for comparing to other such time values returned on the same system. In that case, the larger value indicates a more recent modification time.

If the file does not exist, then a value of 0 is returned.

Returns:

The last modification time of the file

Throws:

SecurityException - If reading of the file is not permitted

length

public long length()

This method returns the length of the file represented by this object, or 0 if the specified file does not exist.

Returns:

The length of the file

Throws:

SecurityException - If reading of the file is not permitted

list

public String[] list(FilenameFilter filter)

This method returns a array of String's representing the list of files is then directory represented by this object. If this object represents a non-directory file or a non-existent file, then null is returned. The list of files will not contain any names such as "." or ".." which indicate the current or parent directory. Also, the names are not guaranteed to be sorted.

In this form of the list() method, a filter is specified that allows the caller to control which files are returned in the list. The FilenameFilter specified is called for each file returned to determine whether or not that file should be included in the list.

A SecurityManager check is made prior to reading the directory. If read access to the directory is denied, an exception will be thrown.

Parameters:

filter - An object which will identify files to exclude from the directory listing.

Returns:

An array of files in the directory, or null if this object does not represent a valid directory.

Throws:

SecurityException - If read access is not allowed to the directory by the SecurityManager

list

public String[] list()

This method returns a array of String's representing the list of files is then directory represented by this object. If this object represents a non-directory file or a non-existent file, then null is returned. The list of files will not contain any names such as "." or ".." which indicate the current or parent directory. Also, the names are not guaranteed to be sorted.

A SecurityManager check is made prior to reading the directory. If read access to the directory is denied, an exception will be thrown.

Returns:

An array of files in the directory, or null if this object does not represent a valid directory.

Throws:

SecurityException - If read access is not allowed to the directory by the SecurityManager

listFiles

public File[] listFiles()

This method returns an array of File objects representing all the files in the directory represented by this object. If this object does not represent a directory, null is returned. Each of the returned File object is constructed with this object as its parent.

A SecurityManager check is made prior to reading the directory. If read access to the directory is denied, an exception will be thrown.

Returns:

An array of File objects for this directory.

Throws:

SecurityException - If the SecurityManager denies access to this directory.

Since:

1.2

listFiles

public File[] listFiles(FilenameFilter filter)

This method returns an array of File objects representing all the files in the directory represented by this object. If this object does not represent a directory, null is returned. Each of the returned File object is constructed with this object as its parent.

In this form of the listFiles() method, a filter is specified that allows the caller to control which files are returned in the list. The FilenameFilter specified is called for each file returned to determine whether or not that file should be included in the list.

A SecurityManager check is made prior to reading the directory. If read access to the directory is denied, an exception will be thrown.

Returns:

An array of File objects for this directory.

Throws:

SecurityException - If the SecurityManager denies access to this directory.

Since:

1.2

listFiles

public File[] listFiles(FileFilter filter)

This method returns an array of File objects representing all the files in the directory represented by this object. If this object does not represent a directory, null is returned. Each of the returned File object is constructed with this object as its parent.

In this form of the listFiles() method, a filter is specified that allows the caller to control which files are returned in the list. The FileFilter specified is called for each file returned to determine whether or not that file should be included in the list.

A SecurityManager check is made prior to reading the directory. If read access to the directory is denied, an exception will be thrown.

Returns:

An array of File objects for this directory.

Throws:

SecurityException - If the SecurityManager denies access to this directory.

Since:

1.2

toString

public String toString()

This method returns a String that is the path name of the file as returned by getPath.

Overrides:

toString in class Object

Returns:

A String representation of this file

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

toURI

public URI toURI()

Returns:

A URI for this object.

toURL

public URL toURL()
          throws MalformedURLException

This method returns a URL with the file: protocol that represents this file. The exact form of this URL is system dependent.

Returns:

A URL for this object.

Throws:

MalformedURLException - If the URL cannot be created successfully.

mkdir

public boolean mkdir()

This method creates a directory for the path represented by this object.

Returns:

true if the directory was created, false otherwise

Throws:

SecurityException - If write access is not allowed to this file

mkdirs

public boolean mkdirs()

This method creates a directory for the path represented by this file. It will also create any intervening parent directories if necessary.

Returns:

true if the directory was created, false otherwise

Throws:

SecurityException - If write access is not allowed to this file

createTempFile

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

This method creates a temporary file in the specified directory. If the directory name is null, then this method uses the system temporary directory. The files created are guaranteed not to currently exist and the same file name will never be used twice in the same virtual machine instance. The system temporary directory is determined by examinging the java.io.tmpdir system property.

The prefix parameter is a sequence of at least three characters that are used as the start of the generated filename. The suffix parameter is a sequence of characters that is used to terminate the file name. This parameter may be null and if it is, the suffix defaults to ".tmp".

If a SecurityManager exists, then its checkWrite method is used to verify that this operation is permitted.

Parameters:

prefix - The character prefix to use in generating the path name.

suffix - The character suffix to use in generating the path name.

directory - The directory to create the file in, or null for the default temporary directory

Throws:

IllegalArgumentException - If the patterns is not valid

SecurityException - If there is no permission to perform this operation

IOException - If an error occurs

Since:

1.2

setReadable

public boolean setReadable(boolean readable)

This method sets the owner's read permission for the File represented by this object. It is the same as calling setReadable(readable, true).

Parameters:

readable - true to set read permission, false to unset the read permission.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setReadable(boolean, boolean)

setReadable

public boolean setReadable(boolean readable,
                  boolean ownerOnly)

This method sets the read permissions for the File represented by this object. If ownerOnly is set to true then only the read permission bit for the owner of the file is changed. If ownerOnly is set to false, the file permissions are changed so that the file can be read by everyone. On unix like systems this sets the user, group and other read bits and is equal to call chmod a+r on the file.

Parameters:

readable - true to set read permission, false to unset the read permission.

ownerOnly - true to set read permission for owner only, false for all.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setReadable(boolean)

setWritable

public boolean setWritable(boolean writable)

This method sets the owner's write permission for the File represented by this object. It is the same as calling setWritable(readable, true).

Parameters:

writable - true to set write permission, false to unset write permission.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setWritable(boolean, boolean)

setWritable

public boolean setWritable(boolean writable,
                  boolean ownerOnly)

This method sets the write permissions for the File represented by this object. If ownerOnly is set to true then only the write permission bit for the owner of the file is changed. If ownerOnly is set to false, the file permissions are changed so that the file can be written by everyone. On unix like systems this set the user, group and other write bits and is equal to call chmod a+w on the file.

Parameters:

writable - true to set write permission, false to unset write permission.

ownerOnly - true to set write permission for owner only, false for all.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setWritable(boolean)

setExecutable

public boolean setExecutable(boolean executable)

This method sets the owner's execute permission for the File represented by this object. It is the same as calling setExecutable(readable, true).

Parameters:

executable - true to set execute permission, false to unset execute permission.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setExecutable(boolean, boolean)

setExecutable

public boolean setExecutable(boolean executable,
                    boolean ownerOnly)

This method sets the execute permissions for the File represented by this object. If ownerOnly is set to true then only the execute permission bit for the owner of the file is changed. If ownerOnly is set to false, the file permissions are changed so that the file can be executed by everyone. On unix like systems this set the user, group and other write bits and is equal to call chmod a+x on the file.

Parameters:

executable - true to set write permission, false to unset write permission.

ownerOnly - true to set write permission for owner only, false for all.

Returns:

true if the file permissions are changed, false otherwise.

Throws:

SecurityException - If write access of the file is not permitted.

Since:

1.6

See Also:

setExecutable(boolean)

setReadOnly

public boolean setReadOnly()

This method sets the file represented by this object to be read only. A read only file or directory cannot be modified. Please note that GNU systems allow read only files to be deleted if the directory it is contained in is writable.

Returns:

true if the operation succeeded, false otherwise.

Throws:

SecurityException - If the SecurityManager does not allow this operation.

Since:

1.2

listRoots

public static File[] listRoots()

This method returns an array of filesystem roots. Some operating systems have volume oriented filesystem. This method provides a mechanism for determining which volumes exist. GNU systems use a single hierarchical filesystem, so will have only one "/" filesystem root.

Returns:

An array of File objects for each filesystem root available.

Since:

1.2

createTempFile

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

This method creates a temporary file in the system temporary directory. The files created are guaranteed not to currently exist and the same file name will never be used twice in the same virtual machine instance. The system temporary directory is determined by examinging the java.io.tmpdir system property.

The prefix parameter is a sequence of at least three characters that are used as the start of the generated filename. The suffix parameter is a sequence of characters that is used to terminate the file name. This parameter may be null and if it is, the suffix defaults to ".tmp".

If a SecurityManager exists, then its checkWrite method is used to verify that this operation is permitted.

This method is identical to calling createTempFile(prefix, suffix, null).

Parameters:

prefix - The character prefix to use in generating the path name.

suffix - The character suffix to use in generating the path name.

Throws:

IllegalArgumentException - If the prefix or suffix are not valid.

SecurityException - If there is no permission to perform this operation

IOException - If an error occurs

compareTo

public int compareTo(File other)

This method compares the specified File to this one to test for equality. It does this by comparing the canonical path names of the files.

The canonical paths of the files are determined by calling the getCanonicalPath method on each object.

This method returns a 0 if the specified Object is equal to this one, a negative value if it is less than this one a positive value if it is greater than this one.

Specified by:

compareTo in interface Comparable<File>

Parameters:

other - the object to be compared

Returns:

An integer as described above

Since:

1.2

renameTo

public boolean renameTo(File dest)

This method renames the file represented by this object to the path of the file represented by the argument File.

Parameters:

dest - The File object representing the target name

Returns:

true if the rename succeeds, false otherwise.

Throws:

SecurityException - If write access is not allowed to the file by the SecurityMananger.

setLastModified

public boolean setLastModified(long time)

This method sets the modification time on the file to the specified value. This is specified as the number of seconds since midnight on January 1, 1970 GMT.

Parameters:

time - The desired modification time.

Returns:

true if the operation succeeded, false otherwise.

Throws:

IllegalArgumentException - If the specified time is negative.

SecurityException - If the SecurityManager will not allow this operation.

Since:

1.2

deleteOnExit

public void deleteOnExit()

Calling this method requests that the file represented by this object be deleted when the virtual machine exits. Note that this request cannot be cancelled. Also, it will only be carried out if the virtual machine exits normally.

Throws:

SecurityException - If deleting of the file is not allowed

Since:

1.2