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 Microsoft Windows UNC pathname, and - A sequence of zero or more string names.
The first name in an abstract pathname may be a directory name or, in the
case of Microsoft Windows UNC pathnames, a hostname. Each subsequent name
in an abstract pathname 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 first name in an abstract pathname may be a directory name or, in the case of Microsoft Windows UNC pathnames, a hostname. Each subsequent name in an abstract pathname 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 separatorseparatorChar
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 parent of an abstract pathname may be obtained by invoking
the getParent() method of this class and consists of the pathname’s
prefix and each name in the pathname’s name sequence except for the last.
Each directory’s absolute pathname is an ancestor of any File
object with an absolute abstract pathname which begins with the directory’s
absolute pathname. For example, the directory denoted by the abstract
pathname "/usr" is an ancestor of the directory denoted by the
pathname "/usr/local/bin".
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 this class may or may not denote an actual file-system
object such as a file or a directory. If it does denote such an object
then that object resides in a partition. A partition is an
operating system-specific portion of storage for a file system. A single
storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
contain multiple partitions. The object, if any, will reside on the
partition named by some ancestor of the absolute
form of this pathname.
A file system may implement restrictions to certain operations on the
actual file-system object, such as reading, writing, and executing. These
restrictions are collectively known as access permissions. The file
system may have multiple sets of access permissions on a single object.
For example, one set may apply to the object’s owner, and another
may apply to all other users. The access permissions on an object may
cause some methods in this class to fail.
Instances of the File class are immutable; that is, once
created, the abstract pathname represented by a File object
will never change.
Interoperability with java.nio.file package
The java.nio.file
package defines interfaces and classes for the Java virtual machine to access
files, file attributes, and file systems. This API may be used to overcome
many of the limitations of the java.io.File class.
The toPath method may be used to obtain a Path that uses the abstract path represented by a File object to
locate a file. The resulting Path may be used with the Files class to provide more efficient and extensive access to
additional file operations, file attributes, and I/O exceptions to help
diagnose errors when an operation on a file fails.
