Java IO.pdf - Nguyen Dang Binh

Java I/O
The details of this format are too complicated to discuss here. You can order the actual
specification [1] from the IEEE for about $29.00. That's approximately $1.50 a page, more than
a little steep in my opinion. The specification isn't available online, but it was published in the
February 1985 issue of ACM SIGPLAN Notices (Volume 22, #2, pp. 9-18), which should be
available in any good technical library. The main thing you need to know is that these formats
are supported by most modern RISC architectures and by all Pentium and Motorola 680x0
chips with either external or internal floating-point units (FPUs). Nowadays the only chips
that don't natively support this format are a few embedded processors and some old 486SX,
68LC040, and other earlier FPU-less chips in legacy hardware. And even these systems are
able to emulate IEEE 754 floating-point arithmetic in software.
The DataInputStream class reads and the DataOutputStream class writes floating-point
numb 1 ers of either four or eight bytes in length, as specified in the IEEE 754 standard. They
do not support the 10-byte and longer long double, extended double, and double double
formats supported by some architectures and compilers. If you have to read floating-point
data written in some format other than basic IEEE 754 float and double, you'll need to write
your own class to convert the format to four- or eight-byte IEEE 754.
7.3.1 Writing Floating-Point Numbers
There are two methods in the DataOutputStream class that write floating-point numbers,
writeFloat() and writeDouble():
public final void writeFloat(float f) throws IOException
public final void writeDouble(double d) throws IOException
Both of these methods throw an IOException if something goes wrong with the underlying
stream. Otherwise, they're fairly innocuous and can convert any float or double to bytes and
write it on the underlying stream.
Example 7.4 fills a file called roots.dat with the square roots of the numbers to 1000. First a
FileOutputStream is opened to roots.dat. This stream is chained to a DataOutputStream,
whose writeDouble() method writes the data into the file.
Example 7.4. Writing Doubles with a DataOutputStream
import java.io.*;
public class RootsFile {
public static void main(String[] args) {
try {
FileOutputStream fout = new FileOutputStream("roots.dat");
DataOutputStream dout = new DataOutputStream(fout);
for (int i = 0; i