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From: lewbloch <lewbloch@gmail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: A question about some long java code that has getters/setters
Date: Sat, 23 Jul 2011 09:02:35 -0700 (PDT)
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Chad wrote:
> 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 {
>
> =A0 =A0 public TestMessagePanel() {
> =A0 =A0 =A0 =A0 MessagePanel messagePanel1 =3D new MessagePanel("Top Left=
");
> =A0 =A0 =A0 =A0 MessagePanel messagePanel2 =3D new MessagePanel("Top Righ=
t");
> =A0 =A0 =A0 =A0 MessagePanel messagePanel3 =3D new MessagePanel("Bottom L=
eft");
> =A0 =A0 =A0 =A0 MessagePanel messagePanel4 =3D new MessagePanel("Bottom R=
ight");
> =A0 =A0 =A0 =A0 messagePanel1.setBackground(Color.RED);
> =A0 =A0 =A0 =A0 messagePanel2.setBackground(Color.CYAN);
> =A0 =A0 =A0 =A0 messagePanel3.setBackground(Color.GREEN);
> =A0 =A0 =A0 =A0 messagePanel4.setBackground(Color.WHITE);
> =A0 =A0 =A0 =A0 messagePanel1.setCentered(true);
>
> =A0 =A0 =A0 =A0 setLayout(new GridLayout(2, 2));
> =A0 =A0 =A0 =A0 add(messagePanel1);
> =A0 =A0 =A0 =A0 add(messagePanel2);
> =A0 =A0 =A0 =A0 add(messagePanel3);
> =A0 =A0 =A0 =A0 add(messagePanel4);
> =A0 =A0 }
>
> =A0 =A0 public static void main(String[] args) {
> =A0 =A0 =A0 =A0 TestMessagePanel frame =3D new TestMessagePanel();
> =A0 =A0 =A0 =A0 frame.setSize(300, 200);
> =A0 =A0 =A0 =A0 frame.setTitle("TestMessagePanel");
> =A0 =A0 =A0 =A0 frame.setLocationRelativeTo(null);
> =A0 =A0 =A0 =A0 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
> =A0 =A0 =A0 =A0 frame.setVisible(true);
>
> =A0 =A0 }//end main()
>
> }
>
> class MessagePanel extends JPanel {
>
> =A0 =A0 private String message =3D "Nope";
> =A0 =A0 private int xCoordinate =3D 20;
> =A0 =A0 private int yCoordinate =3D 20;
> =A0 =A0 private int interval =3D 10;
> =A0 =A0 private boolean centered;
>
> =A0 =A0 public MessagePanel() {
> =A0 =A0 }
>
> =A0 =A0 public MessagePanel(String message) {
> =A0 =A0 =A0 =A0 this.message =3D message;
> =A0 =A0 }
>
> =A0 =A0 public String getMessage() {
> =A0 =A0 =A0 =A0 return message;
> =A0 =A0 }
>
> =A0 =A0 public void setMessage(String message) {
> =A0 =A0 =A0 =A0 this.message =3D message;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public int getXCoordinate() {
> =A0 =A0 =A0 =A0 return xCoordinate;
> =A0 =A0 }
>
> =A0 =A0 public void setXCoordinate(int x) {
> =A0 =A0 =A0 =A0 this.xCoordinate =3D x;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public int getYCoordinate() {
> =A0 =A0 =A0 =A0 return yCoordinate;
> =A0 =A0 }
>
> =A0 =A0 public void setYCoordinate(int y) {
> =A0 =A0 =A0 =A0 this.xCoordinate =3D y;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public boolean isCentered() {
> =A0 =A0 =A0 =A0 return centered;
> =A0 =A0 }
>
> =A0 =A0 public void setCentered(boolean centered) {
> =A0 =A0 =A0 =A0 this.centered =3D centered;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public int getInterval() {
> =A0 =A0 =A0 =A0 return interval;
> =A0 =A0 }
>
> =A0 =A0 public void setInterval(int interval) {
> =A0 =A0 =A0 =A0 this.interval =3D interval;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 protected void paintComponent(Graphics g) {
> =A0 =A0 =A0 =A0 super.paintComponent(g);
>
> =A0 =A0 =A0 =A0 if (centered) {
> =A0 =A0 =A0 =A0 =A0 =A0 FontMetrics fm =3D g.getFontMetrics();
> =A0 =A0 =A0 =A0 =A0 =A0 int stringWidth =3D fm.stringWidth(message);
> =A0 =A0 =A0 =A0 =A0 =A0 int stringAscent =3D fm.getAscent();
> =A0 =A0 =A0 =A0 =A0 =A0 xCoordinate =3D getWidth() / 2 - stringWidth / 2;
> =A0 =A0 =A0 =A0 =A0 =A0 yCoordinate =3D getWidth() / 2 - stringAscent / 2=
;
> =A0 =A0 =A0 =A0 }
> =A0 =A0 =A0 =A0 g.drawString(message, xCoordinate, yCoordinate);
> =A0 =A0 }
>
> =A0 =A0 public void MoveLeft() {
> =A0 =A0 =A0 =A0 xCoordinate -=3D interval;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public void MoveRight() {
> =A0 =A0 =A0 =A0 xCoordinate +=3D interval;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public void moveUp() {
> =A0 =A0 =A0 =A0 yCoordinate -=3D interval;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public void moveDown() {
> =A0 =A0 =A0 =A0 yCoordinate +=3D interval;
> =A0 =A0 =A0 =A0 repaint();
> =A0 =A0 }
>
> =A0 =A0 public Dimension getPreferredSize() {
> =A0 =A0 =A0 =A0 return new Dimension(200, 30);
> =A0 =A0 }
>
> }
>
> 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?

The problem with this code is that it teaches the bad and bug-prone
practice of creating GUI elements on the main thread instead of the
EDT.  Don't use this book.  The author apparently didn't know what he
was doing.

It is standard practice to create accessors and mutators for class
attributes.  There's nothing wrong with that.  The class is written as
any good API writer (a.k.a. "programmer") should in that one respect.
While you should not build features into a class on a remote chance of
their use, if you have properties then you should provide the get/set
methods for them quite nearly always.

But you should never, never, never do GUI magic off the EDT!

It's also bad practice to use import-on-demand (import '*') rather
than single-type imports.

Really, don't use this book.  Get a good book.

--
Lew