The
PrintWriter Class
Although using System.out to write to the console is
acceptable, its use is probably best for debugging purposes or for sample
programs, such as those found in this book. For real-world programs, the
recommended method of writing to the console when using Java is through a PrintWriter stream. PrintWriter is one of the
character-based classes. Using a character-based class for console output makes
internationalizing your program easier.
PrintWriter defines several constructors. The one we will use is shown here: PrintWriter(OutputStream outputStream, boolean flushingOn)
Here, outputStream is an object of type OutputStream, and flushingOn
controls whether Java flushes the output stream every time a println( ) method (among others) is
called. If flushingOn is true,
flushing automatically takes place. If false, flushing is not automatic.
PrintWriter supports the print( ) and println( ) methods. Thus, you can use
these methods in the same way as you
used them with System.out. If an
argument is not a simple type, the PrintWriter
methods call the object’s toString(
) method and then display the result.
To write to the console by
using a PrintWriter, specify System.out for the output stream and
automatic flushing. For example, this line of code creates a PrintWriter that is connected to
console output:
PrintWriter pw = new PrintWriter(System.out,
true);
The following application
illustrates using a PrintWriter to
handle console output:
// Demonstrate PrintWriter import java.io.*;
public class PrintWriterDemo {
public static void main(String args[]) {
PrintWriter pw = new PrintWriter(System.out,
true);
pw.println("This is a string"); int i
= -7;
pw.println(i); double d = 4.5e-7;
pw.println(d);
}
}
The output from this program
is shown here:
This is a string -7
4.5E-7
Remember, there is nothing wrong
with using System.out to write
simple text output to the console when you are learning Java or debugging your
programs. However, using a PrintWriter
makes your real-world applications easier to internationalize. Because no
advantage is gained by using a PrintWriter
in the sample programs shown in this book, we will continue to use System.out to write to the console.
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