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

Chad <cdalten@gmail.com>
Fri, 22 Jul 2011 16:12:27 -0700 (PDT)
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");

        setLayout(new GridLayout(2, 2));

    public static void main(String[] args) {
        TestMessagePanel frame = new TestMessagePanel();
        frame.setSize(300, 200);

    }//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;

    public int getXCoordinate() {
        return xCoordinate;

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

    public int getYCoordinate() {
        return yCoordinate;

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

    public boolean isCentered() {
        return centered;

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

    public int getInterval() {
        return interval;

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

    protected void paintComponent(Graphics 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;

    public void MoveRight() {
        xCoordinate += interval;

    public void moveUp() {
        yCoordinate -= interval;

    public void moveDown() {
        yCoordinate += interval;

    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.



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