Java The Complete Reference, Seventh Edition

294 Part I: The Java Language

Here,fileNamespecifies the name of the file that you want to open. When you create an

input stream, if the file does not exist, thenFileNotFoundExceptionis thrown. For output

streams, if the file cannot be created, thenFileNotFoundExceptionis thrown. When an

output file is opened, any preexisting file by the same name is destroyed.

When you are done with a file, you should close it by callingclose( ). It is defined by

bothFileInputStreamandFileOutputStream, as shown here:

void close( ) throws IOException

To read from a file, you can use a version ofread( )that is defined withinFileInputStream.

The one that we will use is shown here:

int read( ) throws IOException

Each time that it is called, it reads a single byte from the file and returns the byte as an integer

value.read( )returns –1 when the end of the file is encountered. It can throw an IOException.

The following program usesread( )to input and display the contentsof a textfile, thename

of which is specified as a command-line argument. Note thetry/catchblocks that handle

two errors that might occur when this program is used—the specifiedfile notbeingfound

or the user forgetting to include the name of the file. You can use this same approach

whenever you use command-line arguments. Other I/O exceptions that might occur

are simply thrown out ofmain( ), which is acceptable for this simple example. However,

often you will want to handle all I/O exceptions yourself when working with files.

/* Display a text file.

To use this program, specify the name

of the file that you want to see.

For example, to see a file called TEST.TXT,

use the following command line.

java ShowFile TEST.TXT

*/

import java.io.*;

class ShowFile {

public static void main(String args[])

throws IOException

{

int i;

FileInputStream fin;

try {

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException e) {

System.out.println("File Not Found");

return;

} catch(ArrayIndexOutOfBoundsException e) {

System.out.println("Usage: ShowFile File");

return;

}