Java IO.pdf - Nguyen Dang Binh

1.6.4 System.in
Java I/O
System.in is the input stream connected to the console, much as System.out is the output
stream connected to the console. In Unix or C terms, System.in is stdin and can be
redirected from a shell in the same fashion. System.in is the static in field of the
java.lang.System class. It's an instance of java.io.InputStream, at least as far as is
documented.
Past what's documented, System.in is really a java.io.BufferedInputStream.
BufferedInputStream doesn't declare any new methods, just overrides the ones already
declared in java.io.InputStream. Buffered input streams read data in large chunks into a
buffer, then parcel it out in requested sizes. This can be more efficient than reading one
character at a time. Otherwise, it's completely transparent to the programmer.
The main significance of this is that each byte is not presented to be read as the user types it
on System.in. Instead, input enters the program one line at a time. This allows a user typing
into the console to backspace over and correct mistakes. Java does not allow you to put the
console into "raw mode," where each character becomes available as soon as it's typed,
including characters like backspace and delete.
In an application run from the command line, System.in is taken from the window where the
program was started; that is, the console. In applets, the same console window that's used for
System.out is also used for System.in ; however, Internet Explorer has no way to read from
System.in in an applet. In Netscape, the console is turned off by default, and users must
explicitly request that it be turned on.
The user types into the console using the platform's default character set, typically ASCII or
some superset thereof. The data is converted into numeric bytes when read. For example, if
the user types "Hello World!" and hits the return or enter key, the following bytes will be read
from System.in in this order:
72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100, 33, 10, 13
Many programs that run from the command line and read input from System.in require you
to enter the "end of stream" character, also known as the "end of file" or EOF character, to
terminate a program normally. How this is entered is platform-dependent. On Unix and the
Mac, Ctrl-D generally indicates end of stream. On Windows, Ctrl-Z does. In some cases it
may be necessary to type this character alone on a line. That is, you may need to hit
Return/Ctrl-Z or Return/Ctrl-D before Java will recognize the end of stream.
1.6.5 Redirecting System.out, System.in, and System.err
In a shell you often redirect stdout, stdin, or stderr. For example, to specify that output
from the Java program OptimumBattingOrder goes into the file yankees99.out and that input
for that program is read from the file yankees99.tab, you might type:
% java OptimumBattingOrder < yankees99.tab > yankees99.out
Redirection in a DOS shell is the same. It's a little more complicated in graphical
environments, but not particularly difficult. To give one example, the JBindery tool included
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