Java IO.pdf - Nguyen Dang Binh

Java I/O
To read a file, just pass the name of the file into the FileInputStream() constructor. Then
use the read() method as normal. For example, the following code fragment reads the file
README.TXT, then prints it on System.out:
try {
FileInputStream fis = new FileInputStream("README.TXT");
int n;
while ((n = fis.available()) > 0) {
byte[] b = new byte[n];
int result = fis.read(b);
if (result == -1) break;
String s = new String(b);
System.out.print(s);
} // End while
} // End try
catch (IOException e) {System.err.println(e);}
System.out.println();
Java looks for files in the current working directory. Generally, this is the directory you were
in when you typed java program_name to start running the program. You can open a file in a
different directory by passing a full or relative path to the file from the current working
directory. For example, to read the file /etc/hosts no matter which directory is current, you can
do this:
FileInputStream fis = new FileInputStream("/etc/hosts");
Notice that this code depends on Unix-style pathnames. It is not guaranteed to work on
Windows or the Mac, though it might; some runtime environments like Apple's Macintosh
Runtime for Java include extra code to translate from Unix-style filenames to the native style.
If the file you're trying to read does not exist when the FileInputStream object is
constructed, a FileNotFoundException (a subclass of java.io.IOException) is thrown. If
for some other reason a file cannot be read—for example, the current process does not have
read permission for the file—some other kind of IOException is thrown.
Example 4.1 reads filenames from the command line, then copies the named files onto
System.out. The StreamCopier.copy() method from Example 3.3 in the last chapter does
the actual reading and writing. Notice that that method does not care that the input is coming
from a file or going to the console. It works regardless of the type of the input and output
streams it's copying. It will work equally well for other streams still to be introduced,
including ones that did not even exist when StreamCopier was created.
Example 4.1. The FileTyper Program
import java.io.*;
import com.macfaq.io.*;
public class FileTyper {
public static void main(String[] args) {
if (args.length == 0) {
System.err.println("Usage: java FileTyper file1 file2 ...");
return;
}
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