Java IO.pdf - Nguyen Dang Binh

Java I/O
one x-type referring to the same basic type (for instance, "application/x-pict" and
"application/x-macpict" both refer to Macintosh PICT images), and the same x-type may be
used for different purposes by different programs. Nonetheless, since new MIME types are
adopted rather slowly, the x-types are important as well.
12.2 Directories and Paths
Modern operating systems organize files into hierarchical directories. Each directory contains
zero or more files or other directories. Like files, directories have names and attributes,
though—depending on the operating system—those names and attributes may be different
from the attributes allowed for files. For example on the Macintosh, a file or directory name
can be up to 31 bytes long, but a volume name can be no more than 27 bytes long.
12.2.1 Paths and Separators
To specify a file completely, you don't just give its name. You also give the directory the file
lives in. Of course, that directory may itself be inside another directory, which may be in
another directory, until you reach the root of the filesystem. The complete list of directories
from the root to a specified file plus the name of the file itself is called the absolute path to
the file. The exact syntax of absolute paths varies from system to system. Here are a few
examples:
DOS C:\PUBLIC\HTML\JAVAFAQ\INDEX.HTM
Win32 C:\public\html\javafaq\index.html
MacOS Macintosh HD:public:html:javafaq:index.html
Unix /public/html/javafaq/index.html
All three strings reference a file named index.html on the primary hard drive in the javafaq
directory, which is itself in the html directory, which is in the public directory. One obvious
difference is the file separator character. Unix uses a forward slash (/) to separate directories;
DOS-based filesystems, including the variants of Windows and OS/2, use a backslash ( \ );
Macs use a colon (:). Other platforms may use something completely different.
The separator used on a given system is available from the mnemonic constants
java.io.File.separator and java.io.File.separatorChar. File.separatorChar is
the first character of the string File.separator. All operating systems I'm familiar with use
a single character separator string, so these two variables are essentially the same. The
File.separator variable is set from the system property file.separator; that is:
public static final String separator =
System.getProperty("file.separator");
public static final char separatorChar = separator.charAt(0);
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