Java IO.pdf - Nguyen Dang Binh

12.3.3 Listing Information About a File
Java I/O
The File class contains many methods that return particular information about the file. Most
of this information can be gleaned from the path field alone without accessing the filesystem.
Therefore, most of these methods do not throw IOExceptions.
12.3.3.1 Does the file exist? Is it a normal file? Is it a directory?
Since a File object does not necessarily correspond to a real file on the disk, the first question
you'll probably want to ask is whether the file corresponding to the File object actually
exists. This is especially important if you're relying on a user to type a filename rather than
select it from a dialog, because users routinely mistype filenames. The exists() method
returns true if the file named in this file object's path field exists, false if it doesn't:
public boolean exists()
There are two other ways to ask this question. The isFile() method returns true if the file
exists and is not a directory. On the other hand, the isDirectory() method returns true if
the file exists and is a directory.
public boolean isFile()
public boolean isDirectory()
The isDirectory() method does consider Unix symbolic links and Mac aliases to directories
to be directories themselves; it does not consider Windows shortcuts to directories to be
directories. All three of these methods throw a security exception if security manager does not
allow the specified file to be read. In fact, if the file couldn't be read if it did exist, then this
exception is thrown whether or not the file actually exists. Even determining whether or not
certain files exist can be considered to be a security violation. Like most security issues, this
is primarily a problem for applets, not applications.
12.3.3.2 Filename and path
The getName() method takes no arguments and returns the name of the file as a string:
public String getName()
The name does not include any part of the directory in which the file lives. That is, you get
back index.html instead of /public/html/javafaq/index.html. If the file is a directory like
/public/html/javafaq/, only the last name is returned (javafaq in this example).
The getPath() method returns the complete path to the file as stored in the File object's path
field:
public String getPath()
This is merely a get method that returns the path field. Therefore, the path is relative if the
File object was constructed with a relative path and absolute if the File object was
constructed with an absolute path. Furthermore, this method never throws IOExceptions.
Consider Example 12.2. This simple program constructs two File objects, one with a relative
path and one with an absolute path, then prints the name and path of each object.
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