Some useful classes - Multimedia Introduction to Programming Using Java - page 204

The next part reads the file and prints the line lengths, using a loop that
processes one line of a file at a time. There is a difference between reading a file
and reading the keyboard. If there are no more lines to read in a file, function
br.readLine() returns null . But there is no concept of the end of the keyboard,
so the method that reads a line waits until the reader has typed another line.
Note the last statement of the method body,

br.close();
which closes the file, making it impossible to read from it anymore with variable
br . In this program, it is not necessary to include this statement because the pro-
gram will terminate right after this statement anyway. However, in general, it is
a good practice to include it, just in case another part of the program attempts to
open and use the same file.

import java.io.*;
import javax.swing.*;
public class WriteExample {
/** Get an output file name from the user and print two lines on it */
public static void main(String[] args) throws IOException {
PrintStream ps= getWriter();
if (ps == null ) {
System.out.println(" User canceled. Nothing was written.");
return ;

}

// Print two lines on the file
ps.println(" This is the first line.");
ps.println(" This is the second line.");

System.out.println( "File has been written." );
ps.close();

}

/** Obtain a file name from the user, using a JFileChooser , and return
a PrintStream that is linked to it. Return null if the user cancels */
public static PrintStream getWriter() throws IOException {
JFileChooser jd= new JFileChooser();
jd.setDialogTitle("Choose output file");
jd.showSaveDialog( null );
File f= jd.getSelectedFile();

if (f == null ) { return null ; }

return new PrintStream( new FileOutputStream(f));

}

}
Figure 5.7: Print two lines on a file chosen by the user