File is one of the most deceiving classes in the API. It does not represent a file, it does not represent a directory. Remember that creating a File object does not imply you have got a corresponding file or directory in the file system.
A File object represents an abstract path name for a file or directory that may exist (or not) in the file system. Read the API for more details on that. Let's take a look these API:
- public String getPath() returns the name of the File object including the path name, whether relative or absolute.
- public String getAbsolutePath() returns the absolute path name of the File object. If the file contains a relative path name, it figures out what the absolute path name would be and returns it. No IOException is thrown if the path name is impossible under the file system naming convention.
- public String getCanonicalPath() returns an absolute and unique pathname of the File object. An IOException is thrown if the path name is not possible. The precise definition of canonical form is system-dependent, but canonical forms are always absolute.
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 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 characters used for separating directory and file names in a path name are different across different operating systems. The File class provides character constants for the separator character-that is, the character between directory and file names-and also the path separator, which is the character between path names in a path list like the CLASSPATH. The separatorChar variable contains the character that separates file and directory names in a path:
public final static char separatorChar
This character is a / under UNIX, but a \ under Windows NT and Windows 95. The pathSeparatorChar contains the character that separates path names in a path list:
public final static char pathSeparatorChar
This character is ; under Windows NT/95 and : under UNIX.
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