Java IO.pdf - Nguyen Dang Binh

Java I/O
When you call read(), you also have to catch the IOException that it might throw. As I've
observed, input and output are often subject to problems outside of your control: disks fail,
network cables break, and so on. Therefore, virtually any I/O method can throw an
IOException, and read() is no exception. You don't get an IOException if read()
encounters the end of the input stream; in this case, it returns -1. You use this as a flag to
watch for the end of stream. The following code shows how to catch the IOException and
test for the end of the stream:
try {
int[] data = new int[10];
for (int i = 0; i < data.length; i++) {
int datum = System.in.read();
if (datum == -1) break;
data[i] = datum;
}
}
catch (IOException e) {System.err.println("Couldn't read from
System.in!");}
The read() method waits or blocks until a byte of data is available and ready to be read.
Input and output can be slow, so if your program is doing anything else of importance, you
should try to put I/O in its own thread.
read() is declared abstract; therefore, InputStream is abstract. Hence, you can never
instantiate an InputStream directly; you always work with one of its concrete subclasses.
Example 3.1 is a program that reads data from System.in and prints the numeric value of
each byte read on the console using System.out.println(). This program could have been
written more simply; in particular, I could have put all the logic in the main() method without
any trouble. However, this example is the basis for a file-dumping utility that I'll develop
throughout the book, and, therefore, I want a flexible design from the start.
Example 3.1. The StreamPrinter Class
package com.macfaq.io;
import java.io.*;
public class StreamPrinter {
InputStream theInput;
public static void main(String[] args) {
StreamPrinter sr = new StreamPrinter(System.in);
sr.print();
}
public StreamPrinter(InputStream in) {
theInput = in;
}
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