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 [sic]

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

public class TestMessagePanel extends JFrame {

    public TestMessagePanel() {
        MessagePanel messagePanel1 = new MessagePanel("Top Left=

        MessagePanel messagePanel2 = new MessagePanel("Top Righ=

        MessagePanel messagePanel3 = new MessagePanel("Bottom L=

        MessagePanel messagePanel4 = new MessagePanel("Bottom R=

        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?