This chapter is largely devoted to one class:
File class gives you the ability to list directories, obtain
file status, rename and delete files on disk, create directories, and
perform other filesystem operations. Many of these would be considered
"system programming" functions on some operating systems; Java makes
them all as portable as possible.
Note that many of the methods of this class attempt to modify the
permanent file store, or disk filesystem, of the computer you run them
on. Naturally, you might not have permission to change certain files in
certain ways. This can be detected by the Java Virtual Machine's (or the
browser's, in an applet)
SecurityManager, which will throw an instance
of the unchecked exception
SecurityException. But failure can also be
detected by the underlying operating system: if the security manager
approves it, but the user running your program lacks permissions on the
directory, for example, you will either get back an indication (such as
false) or an instance of the checked exception
IOException. This must be caught (or declared
throws clause) in any code
that calls any method that tries to change the filesystem.
You need to know all you can about a given file on disk.
File class has a number of "informational" methods. To use
any of these, you must construct a
File object containing ...