Java IO.pdf - Nguyen Dang Binh

File temp = new File("com");
temp = new File(temp, "macfaq");
temp = new File(temp, "io");
File scfile = new File(temp, "StreamCopier.class");
Java I/O
None of these constructors throw any exceptions. All the constructor does is set the path
field; Java never checks to see whether the file named by path actually exists or even whether
the name passed to the constructor is a valid filename. For example, the following File object
will cause problems on Unix, OS/2, the Mac, and Windows; but you can still construct it:
File f = new File("-This is not a /nice\\ file:\r\nno it isn't");
Some methods in other classes also return File objects, most notably the
java.awt.FileDialog and javax.awt.swing.JFileChooser methods discussed in the next
chapter. Using file dialogs or choosers to ask the user for a filename is preferable to
hardcoding them or reading them from the command line, because file dialogs properly
handle cross-platform issues and the distinctions between relative and absolute paths.
One thing you may not have noticed about these constructors: since a
File object does not represent a file as much as a filename, these
constructors do not actually create files. To create a new file with Java,
you can open a file output stream to the file or invoke the
createNewFile() method. The latter only works in Java 2 and later.
In Java 2 and later, construction of a File object includes normalization. This process reads
hardcoded pathnames and attempts to convert them to the conventions of the local platform.
This improves compatibility with code that's making assumptions about filenames. For
instance, if a Windows VM is asked to create a File object with the path
/public/html/javafaq/course/week2/index.html, it will actually set the path field to \ public\
html\ javafaq\ course\ week2\ index.html. The reverse process happens on Unix; backslashes
are converted to forward slashes. Java 2 is not available for the Mac at the time of this
writing, so it remains to be seen how the Mac will normalize filenames. Because it can only
really normalize separators, not filesystem roots, this scheme works better for relative
pathnames than absolute ones.
12.3.2 Listing the Roots
Java 2 provides a static File.listRoots() method that returns an array of all the available
roots of the filesystem as File objects:
public static File[] listRoots() // Java 2
On Unix, this array is likely to have length 1 and contain the single root /. On Windows, it
will probably contain all the drive letters mapped to one device or another, whether or not
there's actually any media in the drive; e.g., A:\, C:\, D:\, E:\, F:\, G:\. On the Mac, the list
will likely contain only the currently mounted drives, and these are likely to have somewhat
more descriptive names than C:\. If the security manager does not allow the program to read
a particular root, then that root is not included in the returned list. If the security manager does
not allow the program to read any root, then the returned list will have length zero. Do not
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