Java graphics - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 172

Our class implements a custom interface called Outputable .Itholds two
methods print (String) and println (String) :
public interface Outputable {
static final char CR =' \ n';
// A method to print a string
public void print (String str);
// A method to print a string with a carriage return
public void println (String str);
}
These methods are intended to correspond to the print methods in System.out
except that they display their strings on the graphics display rather than on the
console. The code below shows how we implement the Outputable methods
with the JTextArea component:
import java.awt.*;
import javax.swing.*;
/**
*This JPanel subclass holds a JTextArea object in a
*JScrollPane area. It also implements our Outputable
*interface to provide print (String) and println (String)
*methods similar to those in System.out.
**/
public class TextOutputPanel extends JPanel
implements Outputable
{
// A Swing textarea for display of string info
JTextArea fTextArea;
public TextOutputPanel () {
// A BorderLayout would be more appropriate here but
// it isn't discussed until chapter 7.
setLayout (new GridLayout (1,1));
// Create an instance of JTextArea
fTextArea = new JTextArea ();
fTextArea.setEditable (false);
// Add to a scroll pane so that a long list of