Java IO.pdf - Nguyen Dang Binh

}
}
}
Java I/O
Since we're no longer writing to System.out and reading from System.in, it's important to
make sure the streams are closed when we're done. This is a good use for a finally clause, as
we need to make sure the files are closed whether or not the reads and writes succeed.
Java is better about closing files than most languages. As long as the VM doesn't terminate
abnormally, the files will be closed when the program exits. Still, if this class is used inside a
long-running program like a web server, waiting until the program exits isn't a good idea;
other threads and processes may need access to the files.
There is one bug in this program: it does not behave well if the input and output files are the
same. While it would be straightforward to compare the two filenames before copying, this is
not safe enough. Once aliases, shortcuts, symbolic links, and other factors are taken into
account, a single file may have multiple names. The full solution to this problem will have to
wait until Chapter 12, when we discuss canonical paths and temporary files.
4.3 File Viewer, Part 1
I often find it useful to be able to open an arbitrary file and interpret it in an arbitrary fashion.
Most commonly I want to view a file as text, but occasionally it's useful to interpret it as
hexadecimal integers, IEEE 754 floating-point data, or something else. In this book, I'm going
to develop a program that lets you open any file and view its contents in a variety of different
ways. In each chapter, I'll add a piece to the program until it's fully functional. Since this is
only the beginning of the program, it's important to keep the code as general and adaptable as
possible.
Example 4.3 reads a series of filenames from the command line in the main() method. Each
filename is passed to a method that opens the file. The file's data is read and printed on
System.out. Exactly how the data is printed on System.out is determined by a commandline
switch. If the user selects ASCII format (-a), then the data will be assumed to be ASCII
(more properly, ISO Latin-1) text and printed as chars. If the user selects decimal dump (-d),
then each byte should be printed as unsigned decimal numbers between and 255, 16 to a line.
For example:
000 234 127 034 234 234 000 000 000 002 004 070 000 234 127 098
Leading zeros are used to maintain a constant width for the printed byte values and for each
line. A simple selection algorithm is used to determine how many leading zeros to attach to
each number. For hex dump format (-h), each byte should be printed as two hexadecimal
digits. For example:
CA FE BA BE 07 89 9A 65 45 65 43 6F F6 7F 8F EE E5 67 63 26 98 9E 9C
Hexadecimal encoding is easier, because each byte is always exactly two hex digits. The
static Integer.toHexString() method is used to convert each byte read into two
hexadecimal digits.
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