EXCEPTION HANDLING AND TEXT I/O - Introduction to Java Programming: Comprehensive Version - page 477

9 // Create a file
10 java.io.PrintWriter output = new java.io.PrintWriter(file);
11
12 // Write formatted output to the file
13 output.print( "John T Smith " );
14 output.println( 90 );
15 output.print( "Eric K Jones " );
16 output.println( 85 );
17
18 // Close the file
19 output.close();
20

create PrintWriter

print data

John T Smith 90
Eric K Jones 85

scores.txt

close file

}

21 }

Lines 4-7 check whether the file scores.txt exists. If so, exit the program (line 6).
Invoking the constructor of PrintWriter will create a new file if the file does not exist. If the
file already exists, the current content in the file will be discarded without verifying with the user.
Invoking the constructor of PrintWriter may throw an I/O exception. Java forces you to write
the code to deal with this type of exception. For simplicity, we declare throws IOException in
the main method header (line 2).
You have used the System.out.print , System.out.println , and System.out.
printf methods to write text to the console. System.out is a standard Java object for the
console output. You can create PrintWriter objects for writing text to any file using print ,
println , and printf (lines 13-16).
The close() method must be used to close the file (line 19). If this method is not invoked,
the data may not be saved properly in the file.

create a file

throws IOException

print method

close file

12.11.2 Closing Resources Automatically Using try-with-resources
Programmers often forget to close the file. JDK 7 provides the followings new try-with-
resources syntax that automatically closes the files.

try (declare and create resources) {
Use the resource to process the file;
}

Using the try-with-resources syntax, we rewrite the code in Listing 12.13 in Listing 12.14.

L ISTING 12.14

WriteDataWithAutoClose.java
1 public class WriteDataWithAutoClose {
2 public static void main(String[] args) throws Exception {
3 java.io.File file = new java.io.File( "scores.txt" );
4 if (file.exists()) {
5 System.out.println( "File already exists" );
6 System.exit( 0 );
7 }
8
9 try (
10 // Create a file
11 java.io.PrintWriter output = new java.io.PrintWriter(file);
12 ) {
13 // Write formatted output to the file
14 output.print( "John T Smith " );
15 output.println( 90 );
16 output.print( "Eric K Jones " );
17 output.println( 85 );
18 }
19 }
20 }

declare/create resource

use the resouce