Thread: Newbeginner - Something wrong with my GUI chess pattern

Hello everyone,

I'm new at programming but everyone starts as newbeginner, right? I'm supposed to make chess patterns on a panel in different sizes but something goes wrong.

It work fine but it doesn't. I think I'm missing something but what I don't know.

Here's the code:

import java.awt.*;
 
public class ChessPattern {
 
	public static void main(String[] args0){
 
		DrawingPanel panel = new DrawingPanel(420, 300);
		panel.setBackground(Color.darkGray);
 
		Graphics g = panel.getGraphics();
 
		square(g, 0, 0, 10, 5, 5);
		square(g, 210, 30, 15, 4, 4);
		square(g, 60, 40, 15, 7, 7);
 
	}
		//method to draw chess pattern squares
		public static void square(Graphics g, int x, int y, int size, int squarecolumn, int squarerow){
			//the column
			for(int j = 0; j < squarecolumn; j++){
				//the row
				for(int i = 0; i < squarerow; i++){
					//if i is even for row and column then gray
					if(i%2 == 0 && j%2 == 0){
						g.setColor(Color.gray);
						//if i is odd for row and column then gray 
					}else if(i%2 == 1 && j%2 == 1){
						g.setColor(Color.gray);
						//if i is even for row and j is odd for column then white
					}else if(i%2 == 0 && j%2 == 1){
						g.setColor(Color.white);
						//if i is odd for row and j is even for column then white
					}else if(i%2 == 1 && j%2 == 0){
						g.setColor(Color.white);
					}
					//where and how much to fill going by row
					g.fillRect(x+i*size,y+j*size, size, size);
 
				}
				//where and how much to fill going by column
				g.fillRect(x, y+j*size, size, size);
 
			}
			//Drawing the reactangle border
			g.setColor(Color.black);
			g.drawRect(x, y, size*squarecolumn, size*squarerow);
 
		}	
}

and here't how it looks:



I found out that everytime I let the squares be even x even size then I get a pattern like the right while odd x odd size gets me the chess pattern I want.

Ex: square(g, 0, 0, 10, 5, 5);
square(g, 210, 30, 15, 4, 4);
square(g, 60, 40, 15, 7, 7);

Could someone help me out and tell/explain me what I am missing or doing wrong?
Thanks^^

PS: For people who wants the DrawingPanel class which was on the CD as support to GUI programming:

/*
Stuart Reges and Marty Stepp
07/01/2005
 
The DrawingPanel class provides a simple interface for drawing persistent
images using a Graphics object.  An internal BufferedImage object is used
to keep track of what has been drawn.  A client of the class simply
constructs a DrawingPanel of a particular size and then draws on it with
the Graphics object, setting the background color if they so choose.
 
To ensure that the image is always displayed, a timer calls repaint at
regular intervals.
*/
 
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.imageio.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class DrawingPanel implements ActionListener {
    public static final int DELAY = 250;  // delay between repaints in millis
 
    private static final String DUMP_IMAGE_PROPERTY_NAME = "drawingpanel.save";
    private static String TARGET_IMAGE_FILE_NAME = null;
    private static final boolean PRETTY = true;  // true to anti-alias
    private static boolean DUMP_IMAGE = false;  // true to write DrawingPanel to file
 
    private int width, height;    // dimensions of window frame
    private JFrame frame;         // overall window frame
    private JPanel panel;         // overall drawing surface
    private BufferedImage image;  // remembers drawing commands
    private Graphics2D g2;        // graphics context for painting
    private JLabel statusBar;     // status bar showing mouse position
    private long createTime;
 
    static {
        TARGET_IMAGE_FILE_NAME = System.getProperty(DUMP_IMAGE_PROPERTY_NAME);
        DUMP_IMAGE = (TARGET_IMAGE_FILE_NAME != null);
    }
 
    // construct a drawing panel of given width and height enclosed in a window
    public DrawingPanel(int width, int height) {
        this.width = width;
        this.height = height;
        this.image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
 
        this.statusBar = new JLabel(" ");
        this.statusBar.setBorder(BorderFactory.createLineBorder(Color.BLACK));
 
        this.panel = new JPanel(new FlowLayout(FlowLayout.CENTER, 0, 0));
        this.panel.setBackground(Color.WHITE);
        this.panel.setPreferredSize(new Dimension(width, height));
        this.panel.add(new JLabel(new ImageIcon(image)));
 
        // listen to mouse movement
        MouseInputAdapter listener = new MouseInputAdapter() {
            public void mouseMoved(MouseEvent e) {
                DrawingPanel.this.statusBar.setText("(" + e.getX() + ", " + e.getY() + ")");
            }
 
            public void mouseExited(MouseEvent e) {
                DrawingPanel.this.statusBar.setText(" ");
            }
        };
        this.panel.addMouseListener(listener);
        this.panel.addMouseMotionListener(listener);
 
        this.g2 = (Graphics2D)image.getGraphics();
        this.g2.setColor(Color.BLACK);
        if (PRETTY) {
            this.g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            this.g2.setStroke(new BasicStroke(1.1f));
        }
 
        this.frame = new JFrame("Drawing Panel");
        this.frame.setResizable(false);
        this.frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                if (DUMP_IMAGE) {
                    DrawingPanel.this.save(TARGET_IMAGE_FILE_NAME);
                }
                System.exit(0);
            }
        });
        this.frame.getContentPane().add(panel);
        this.frame.getContentPane().add(statusBar, "South");
        this.frame.pack();
        this.frame.setVisible(true);
        if (DUMP_IMAGE) {
            createTime = System.currentTimeMillis();
            this.frame.toBack();
        } else {
            this.toFront();
        }
 
        // repaint timer so that the screen will update
        new Timer(DELAY, this).start();
    }
 
    // used for an internal timer that keeps repainting
    public void actionPerformed(ActionEvent e) {
        this.panel.repaint();
        if (DUMP_IMAGE && System.currentTimeMillis() > createTime + 4 * DELAY) {
            this.frame.setVisible(false);
            this.frame.dispose();
            this.save(TARGET_IMAGE_FILE_NAME);
            System.exit(0);
        }
    }
 
    // obtain the Graphics object to draw on the panel
    public Graphics2D getGraphics() {
        return this.g2;
    }
 
    // set the background color of the drawing panel
    public void setBackground(Color c) {
        this.panel.setBackground(c);
    }
 
    // show or hide the drawing panel on the screen
    public void setVisible(boolean visible) {
        this.frame.setVisible(visible);
    }
 
    // makes the program pause for the given amount of time,
    // allowing for animation
    public void sleep(int millis) {
        try {
            Thread.sleep(millis);
        } catch (InterruptedException e) {}
    }
 
    // take the current contents of the panel and write them to a file
    public void save(String filename) {
        String extension = filename.substring(filename.lastIndexOf(".") + 1);
 
        // create second image so we get the background color
        BufferedImage image2 = new BufferedImage(this.width, this.height, BufferedImage.TYPE_INT_RGB);
        Graphics g = image2.getGraphics();
        g.setColor(panel.getBackground());
        g.fillRect(0, 0, this.width, this.height);
        g.drawImage(this.image, 0, 0, panel);
 
        // write file
        try {
            ImageIO.write(image2, extension, new java.io.File(filename));
        } catch (java.io.IOException e) {
            System.err.println("Unable to save image:\n" + e);
        }
    }
 
    // makes drawing panel become the frontmost window on the screen
    public void toFront() {
        this.frame.toFront();
    }
}

Just have time for a quick glance but immediately see something amiss - do not paint to a graphics object of a Swing component by calling getGraphics(): place all your painting routines in the paintComponent method (see Painting in AWT and Swing ) Whether not this is directly your problem I can't say right now, but I'd highly recommend adjusting your code to paint the recommended way first, then re-post the code if you still have issues

I'm curious what book you have: if it teaches you to paint to swing components in this way the author has lost all credibility with me. I know this isn't directly the problem, but it is best practice. You can listen to your book, or some stranger on the internet: your choice

Now that I've had more time to look at the code, why is there the second fillRect call at the end of your inside for loop (with i)? Comment out that line and see what happens...