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java.io
Class File

java.lang.Object
  java.io.File

All Implemented Interfaces:: java.lang.Comparable, Serializable

public class File
extends java.lang.Object
implements Serializable, java.lang.Comparable

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.

Field Summary

private static java.lang.String dupSeparator


private static long last_tmp
          The time (millisecond), when the last temporary file was created.

private static int n_created
          The number of files, created during the current millisecond.

private java.lang.String path
          This is the path to the file set when the object is created.

static java.lang.String pathSeparator
          This is the string that is used to separate the host name from the path name in paths than 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 java.lang.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.

private static long serialVersionUID


Constructor Summary

File(File directory, java.lang.String name)
          This method initializes a new File object to represent a file in the specified directory.

File(java.lang.String name)
          This method initializes a new File object to represent a file with the specified path.

File(java.lang.String dirPath, java.lang.String name)
          This method initializes a new File object to represent a file in the specified named directory.

File(java.net.URI uri)
          This method initializes a new File object to represent a file corresponding to the specified file: protocol URI.

Method Summary

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.

private void checkRead()


private void checkWrite()


int compareTo(File other)
          This method compares the specified File to this one to test for equality.

int compareTo(java.lang.Object obj)
          This method compares the specified Object 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(java.lang.String prefix, java.lang.String suffix)
          This method creates a temporary file in the system temporary directory.

static File createTempFile(java.lang.String prefix, java.lang.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(java.lang.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.

java.lang.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.

java.lang.String getCanonicalPath()
          This method returns a canonical representation of the pathname of this file.

java.lang.String getName()
          This method returns the name of the file.

java.lang.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.

java.lang.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.

java.lang.String[] list()
          This method returns a array of String's representing the list of files is then directory represented by this object.

java.lang.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.

private java.lang.String normalizePath(java.lang.String p)


private void readObject(ObjectInputStream ois)


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 setLastModified(long time)
          This method sets the modification time on the file to the specified value.

boolean setReadOnly()
          This method sets the file represented by this object to be read only.

java.lang.String toString()
          This method returns a String that is the path name of the file as returned by getPath.

java.net.URI toURI()


java.net.URL toURL()
          This method returns a URL with the file: protocol that represents this file.

private void writeObject(ObjectOutputStream oos)


Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:: Constant Field Values

separator

public static final java.lang.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.

dupSeparator

private static final java.lang.String dupSeparator

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 java.lang.String pathSeparator

This is the string that is used to separate the host name from the path name in paths than 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.

path

private java.lang.String path

This is the path to the file set when the object is created. It may be an absolute or relative path name.

last_tmp

private static long last_tmp

The time (millisecond), when the last temporary file was created.

n_created

private static int n_created

The number of files, created during the current millisecond.

Constructor Detail

File

public File(java.lang.String name)

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

File

public File(java.lang.String dirPath,
            java.lang.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.

File

public File(File directory,
            java.lang.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

File

public File(java.net.URI uri)

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

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.

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.

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.

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.

equals

public boolean equals(java.lang.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.

exists

public boolean exists()

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

normalizePath

private java.lang.String normalizePath(java.lang.String p)

getAbsolutePath

public java.lang.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.

getAbsoluteFile

public File getAbsoluteFile()

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

Since:: 1.2

getCanonicalPath

public java.lang.String getCanonicalPath()
                                  throws IOException

This method returns a canonical representation of the pathname of this file. The actual form of the canonical representation is different. On the GNU system, the canonical form differs from the absolute form in that all relative file references to "." and ".." are resolved and removed.

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

getCanonicalFile

public File getCanonicalFile()
                      throws IOException

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

Since:: 1.2

getName

public java.lang.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.

getParent

public java.lang.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

getParentFile

public File getParentFile()

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

Since:: 1.2

getPath

public java.lang.String getPath()

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

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.

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 "/".

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.

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.

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.

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.

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.

list

public java.lang.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.