Java IO.pdf - Nguyen Dang Binh

Java I/O
If you need to know whether a file is specified by a relative or absolute path, you can call
isAbsolute():
public boolean isAbsolute()
This does not throw any security exceptions, because it does not need to go outside the class
to determine whether or not a pathname is absolute. Instead, the check is performed by
looking at the first few characters of the path field. On Unix or the Mac an absolute path
begins with a /. On Windows or OS/2 an absolute path begins with a capital letter followed by
a colon and a backslash, like C:\.
12.3.3.4 Canonical paths
Exactly what a canonical path is, and how it differs from an absolute path, is systemdependent,
but it tends to mean that the path is somehow more real than the absolute path.
Typically, if the full path contains aliases, shortcuts, shadows, or symbolic links of some kind,
the canonical path resolves those aliases to the actual directories they refer to. The canonical
path is returned by the getCanonicalPath() method:
public String getCanonicalPath() throws IOException
For example, on Unix when getAbsolutePath() is invoked on a symbolic link or a file that
has a symbolic link (an alias or shortcut) in its path, the symbolic link is included in the path
that getAbsolutePath() returns. However getCanonicalPath() returns the path with all
symbolic links resolved. For example, suppose /bin/perl is a link to the real file at
/usr/local/bin/perl, and you construct a File object perlLink like this:
File perlLink = new File("/bin/perl");
perlLink.getAbsolutePath() returns /bin/perl, but perlLink.getCanonicalPath()
returns /usr/local/bin/perl.
On Windows and the Macintosh, getAbsolutePath() and getCanonicalPath() both
resolve shortcuts and aliases. Suppose /Macintosh%20HD/Desktop%20Folder/javac is an
alias to /Macintosh%20HD/Java/MRJ%202.0%20Early%20Access%
20Rel%202/MRJ%20SDK%202.0/Tools/javac, and a File object named alias is constructed
like this:
File alias = new File("/Macintosh%20HD/Desktop%20Folder/javac");
Both alias.getAbsolutePath() and alias.getCanonicalPath() return
/Macintosh%20HD/Java/MRJ%202.0%20Early%20Access%20Rel%202/MRJ%20SDK%202.
0/Tools/javac, not /Macintosh%20HD/Desktop%20Folder/javac . getCanonicalPath()
throws a security exception in most applet environments, because it reveals too much
information about the host the applet is running on. getCanonicalPath() also removes
relative references like the double period (..), which refers to the parent directory in many
command-line environments and in URLs. For instance, suppose the current working
directory is /home/users/elharo/javaio/ioexamples/12. Then you create a File object like this:
File f = new File("../11/index.html");
String absolutePath = f.getAbsolutePath();
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