Java Doc for File.java in  » 6.0-JDK-Modules » j2me » java » io » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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:

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

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 File.separator and File.separatorChar of this class. When a pathname string is converted into an abstract pathname, the names within it may be separated by the default name-separator character or by any other name-separator character that is supported by the underlying system.

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

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

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

Instances of the File class are immutable; that is, once created, the abstract pathname represented by a File object will never change.
version:
   1.116, 08/01/03
author:
   unascribed
since:
   JDK1.0

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 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.

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

For a given abstract pathname f it is guaranteed that

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

Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name.

If this abstract pathname is already absolute, then the pathname string is simply returned as if by the File.getPath method.

A canonical pathname is both absolute and unique.

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.

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 this abstract pathname does not denote a directory, then this method returns null.

If this abstract pathname does not denote a directory, then this method returns null.

A particular Java platform may support zero or more hierarchically-organized file systems.

Whether or not this method can move a file from one filesystem to another is platform-dependent.

All platforms support file-modification times to the nearest second, but some provide more precision.

The exact form of the URI is system-dependent.

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
Parameters:
  child - The child pathname string
throws:
  NullPointerException - If child is null

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
Parameters:
  child - The child pathname string
throws:
  NullPointerException - If child is null

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

For a given abstract pathname f it is guaranteed that

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

Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. true if the named file does not exist and wassuccessfully created; false if the named filealready exists
throws:
  IOException - If an I/O error occurred
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkWrite(java.lang.String)method denies write access to the file
since:
   1.2

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:

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

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 Microsoft Windows systems it is typically "c:\\temp". A different value may be given to this system property when the Java virtual machine is invoked, but programmatic changes to this property are not guaranteed to have any effect upon the the temporary directory used by this method.
Parameters:
  prefix - The prefix string to be used in generating the file'sname; must be at least three characters long
Parameters:
  suffix - The suffix string to be used in generating the file'sname; may be null, in which case thesuffix ".tmp" will be used
Parameters:
  directory - The directory in which the file is to be created, ornull if the default temporary-filedirectory is to be used An abstract pathname denoting a newly-created empty file
throws:
  IllegalArgumentException - If the prefix argument contains fewer than threecharacters
throws:
  IOException - If a file could not be created
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkWrite(java.lang.String)method does not allow a file to be created
since:
   1.2

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

Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably.
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkDelete method deniesdelete access to the file
See Also:   File.delete
since:
   1.2

If this abstract pathname is already absolute, then the pathname string is simply returned as if by the File.getPath method. If this abstract pathname is the empty abstract pathname then the pathname string of the current user directory, which is named by the system property user.dir, is returned. Otherwise this pathname is resolved in a system-dependent way. On UNIX systems, a relative pathname is made absolute by resolving it against the current user directory. On Microsoft Windows systems, a relative pathname is made absolute by resolving it against the current directory of the drive named by the pathname, if any; if not, it is resolved against the current user directory. The absolute pathname string denoting the same file ordirectory as this abstract pathname
throws:
  SecurityException - If a required system property value cannot be accessed.
See Also:   java.io.File.isAbsolute

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

Every pathname that denotes an existing file or directory has a unique canonical form. Every pathname that denotes a nonexistent file or directory also has a unique canonical form. The canonical form of the pathname of a nonexistent file or directory may be different from the canonical form of the same pathname after the file or directory is created. Similarly, the canonical form of the pathname of an existing file or directory may be different from the canonical form of the same pathname after the file or directory is deleted. The canonical pathname string denoting the same file ordirectory as this abstract pathname
throws:
  IOException - If an I/O error occurs, which is possible because theconstruction of the canonical pathname may requirefilesystem queries
throws:
  SecurityException - If a required system property value cannot be accessed.
since:
   JDK1.1

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. The pathname string of the parent directory named by thisabstract pathname, or null if this pathnamedoes not name a parent

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. The abstract pathname of the parent directory named by thisabstract pathname, or null if this pathnamedoes not name a parent
since:
   1.2

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

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(java.io.File,java.lang.String)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. An array of abstract pathnames denoting the files anddirectories in the directory denoted by this abstractpathname. The array will be empty if the directory isempty. Returns null if this abstract pathnamedoes not denote a directory, or if an I/O error occurs.
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkRead(java.lang.String)method denies read access to the directory
since:
   1.2

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 java.lang.SecurityManager.checkRead(java.lang.String) method denies read access to a particular root directory, then that directory will not appear in the result. An array of File objects denoting the availablefilesystem roots, or null if the set of rootscould not be determined. The array will be empty if there areno filesystem roots.
since:
   1.2

Whether or not this method can move a file from one filesystem to another is platform-dependent. The return value should always be checked to make sure that the rename operation was successful.
Parameters:
  dest - The new abstract pathname for the named file true if and only if the renaming succeeded;false otherwise
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkWrite(java.lang.String)method denies write access to either the old or new pathnames
throws:
  NullPointerException - If parameter dest is null

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 File.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 sincethe epoch (00:00:00 GMT, January 1, 1970) true if and only if the operation succeeded;false otherwise
throws:
  IllegalArgumentException - If the argument is negative
throws:
  SecurityException - If a security manager exists and its java.lang.SecurityManager.checkWrite(java.lang.String)method denies write access to the named file
since:
   1.2

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

For a given abstract pathname f, it is guaranteed that

new File.File(java.net.URI) File ( f.toURI()).equals( f. File.getAbsoluteFile() getAbsoluteFile ())

Usage note: This method does not automatically escape characters that are illegal in URLs. It is recommended that new code convert an abstract pathname into a URL by first converting it into a URI, via the File.toURI() toURI method, and then converting the URI into a URL via the java.net.URI.toURL URI.toURL method. A URL object representing the equivalent file URL
throws:
  MalformedURLException - If the path cannot be parsed as a URL
See Also:   File.toURI()
See Also:   java.net.URI
See Also:   java.net.URI.toURL
See Also:   java.net.URL
since:
   1.2