Re: A question about some long java code that has getters/setters

The following code, which is taken from one of my school books,
displays 4 different boxes inside a gui

import java.awt.*;
import javax.swing.*;

public class TestMessagePanel extends JFrame {

     public TestMessagePanel() {
         MessagePanel messagePanel1 = new MessagePanel("Top Left");
         MessagePanel messagePanel2 = new MessagePanel("Top Right");
         MessagePanel messagePanel3 = new MessagePanel("Bottom Left");
         MessagePanel messagePanel4 = new MessagePanel("Bottom Right");
         messagePanel1.setBackground(Color.RED);
         messagePanel2.setBackground(Color.CYAN);
         messagePanel3.setBackground(Color.GREEN);
         messagePanel4.setBackground(Color.WHITE);
         messagePanel1.setCentered(true);

         setLayout(new GridLayout(2, 2));
         add(messagePanel1);
         add(messagePanel2);
         add(messagePanel3);
         add(messagePanel4);
     }

     public static void main(String[] args) {
         TestMessagePanel frame = new TestMessagePanel();
         frame.setSize(300, 200);
         frame.setTitle("TestMessagePanel");
         frame.setLocationRelativeTo(null);
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         frame.setVisible(true);

     }//end main()
}

class MessagePanel extends JPanel {

     private String message = "Nope";
     private int xCoordinate = 20;
     private int yCoordinate = 20;
     private int interval = 10;
     private boolean centered;

     public MessagePanel() {
     }

     public MessagePanel(String message) {
         this.message = message;
     }

     public String getMessage() {
         return message;
     }

     public void setMessage(String message) {
         this.message = message;
         repaint();
     }

     public int getXCoordinate() {
         return xCoordinate;
     }

     public void setXCoordinate(int x) {
         this.xCoordinate = x;
         repaint();
     }

     public int getYCoordinate() {
         return yCoordinate;
     }

     public void setYCoordinate(int y) {
         this.xCoordinate = y;
         repaint();
     }

     public boolean isCentered() {
         return centered;
     }

     public void setCentered(boolean centered) {
         this.centered = centered;
         repaint();
     }

     public int getInterval() {
         return interval;
     }

     public void setInterval(int interval) {
         this.interval = interval;
         repaint();
     }

     protected void paintComponent(Graphics g) {
         super.paintComponent(g);

         if (centered) {
             FontMetrics fm = g.getFontMetrics();
             int stringWidth = fm.stringWidth(message);
             int stringAscent = fm.getAscent();
             xCoordinate = getWidth() / 2 - stringWidth / 2;
             yCoordinate = getWidth() / 2 - stringAscent / 2;
         }
         g.drawString(message, xCoordinate, yCoordinate);
     }

     public void MoveLeft() {
         xCoordinate -= interval;
         repaint();
     }

     public void MoveRight() {
         xCoordinate += interval;
         repaint();
     }

     public void moveUp() {
         yCoordinate -= interval;
         repaint();
     }

     public void moveDown() {
         yCoordinate += interval;
         repaint();
     }

     public Dimension getPreferredSize() {
         return new Dimension(200, 30);
     }
}

What I don't get is why the book defines stuff like getXCoordinate(),
getYCoordinate(), and getInterval() when it doesn't even use them in
this very long code example. I tried reading over the section in the
book, but the author gives no explanation on why he included a bunch
of unused getters/setters. On top of that, the code seems to work fine
when I comment out these methods.

Ideas?