Java Reference
In-Depth Information
end-of-file indication occurs as an exception. In others, the indication is a return value
from a method invoked on a stream-processing object.
0123456789 .
...
n-1
end-of-file marker
Fig. 15.1
|
Java's view of a file of
n
bytes.
Byte-Based and Character-Based Streams
File streams can be used to input and output data as bytes or characters.
•
Byte-based streams
output and input data in its
binary
format—a
char
is two
bytes, an
int
is four bytes, a
double
is eight bytes, etc.
•
Character-based streams
output and input data as a
sequence of characters
in
which every character is two bytes—the number of bytes for a given value de-
pends on the number of characters in that value. For example, the value
2000000000
requires 20 bytes (10 characters at two bytes per character) but the
value
7
requires only two bytes (1 character at two bytes per character).
Files created using byte-based streams are referred to as
binary files
, while files created us-
ing character-based streams are referred to as
text files
. Text files can be read by text edi-
tors, while binary files are read by programs that understand the file's specific content and
its ordering. A numeric value in a binary file can be used in calculations, whereas the char-
acter
5
is simply a character that can be used in a string of text, as in
"Sarah
Miller
is
15
years
old"
.
Standard Input, Standard Output and Standard Error Streams
A Java program
opens
a file by creating an object and associating a stream of bytes or char-
acters with it. The object's constructor interacts with the operating system to
open
the file.
Java can also associate streams with different devices. When a Java program begins execut-
ing, it creates three stream objects that are associated with devices—
System.in
,
Sys-
tem.out
and
System.err
. The
System.in
(standard input stream) object normally enables
a program to input bytes from the keyboard. Object
System.out
(the standard output
stream object) normally enables a program to output character data to the screen. Object
System.err
(the standard error stream object) normally enables a program to output char-
acter-based error messages to the screen. Each stream can be
redirected
. For
System.in
,
this capability enables the program to read bytes from a different source. For
System.out
and
System.err
, it enables the output to be sent to a different location, such as a file on
disk. Class
System
provides methods
setIn
,
setOut
and
setErr
to redirected the standard
input, output and error streams, respectively.
The
java.io
and
java.nio
Packages
Java programs perform stream-based processing with classes and interfaces from package
java.io
and the subpackages of
java.nio
—Java's New I/O APIs that were first intro-
duced in Java SE 6 and that have been enhanced since. There are also other packages
throughout the Java APIs containing classes and interfaces based on those in the
java.io
and
java.nio
packages.
