How to fix chess board squares not moving to middle

Question

at the moment I try to make a chessboard with fix sizes. I successfully make that the chessboard will be painted in the corner (coordinate 0,0,400,400). However, now I want that the chessboard will always be in the middle also if I move the window. The background of the chessboard moves always and is always in the middle but the squares are fixed. To make you understand my problem, I upload some pics where you can see my main issue.

First Start:

Moving the window to the left

Background in the middle but without the white squares JPanel

import java.awt.Color;
import java.awt.Graphics;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author Serge Junk
 */
public class DrawPanel extends javax.swing.JPanel {

    /**
     * Creates new form DrawPanel
     */
    public DrawPanel() {
        initComponents();
    }

    @Override
      public void paintComponent(Graphics g)
    {
        int width = (getWidth() - 400)/2;
        int height = (getHeight()- 400)/2;

        g.setColor(Color.white);
        g.fillRect(0, 0, getWidth(), getHeight());

        g.setColor(Color.gray);
        g.fillRect(width, height, 400, 400);

        g.setColor(Color.black);
        g.drawRect(width, height, 400, 400);

        for(int i=width;i<400;i+=100)
        {
            for(int j=height;j<400;j+=100)
            {
                g.setColor(Color.white);
                g.fillRect(i, j, 50, 50); 
                g.setColor(Color.black);
                g.drawRect(i, j, 50, 50);
            }

        }
        for(int i=width+50;i<400;i+=100)
        {
            for(int j=height+50;j<400;j+=100)
            {
                g.setColor(Color.white);
                g.fillRect(i, j, 50, 50);
                g.setColor(Color.black);
                g.drawRect(i, j, 50, 50);
            }
        }
    }

    /**
     *
     */
    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );
    }// </editor-fold>                        


    // Variables declaration - do not modify                     
    // End of variables declaration                   
}

JFrame

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author Serge Junk
 */
public class MainFrame extends javax.swing.JFrame {

    /**
     * Creates new form MainFrame
     */
    public MainFrame() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        drawPanel1 = new DrawPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.GroupLayout drawPanel1Layout = new javax.swing.GroupLayout(drawPanel1);
        drawPanel1.setLayout(drawPanel1Layout);
        drawPanel1Layout.setHorizontalGroup(
            drawPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 652, Short.MAX_VALUE)
        );
        drawPanel1Layout.setVerticalGroup(
            drawPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 473, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(drawPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(drawPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>                        

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new MainFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private DrawPanel drawPanel1;
    // End of variables declaration                   
}

Answer 1

You can achieve it with a twice smaller code:

for (int i = width; i < 400 + width; i += 100) {
   for (int j = height; j < 400 + height; j += 100) {
            g.setColor(Color.white);
            g.fillRect(i, j, 50, 50);
            g.fillRect(i+50, j+50, 50, 50);
            g.setColor(Color.black);
            g.drawRect(i, j, 50, 50);
            g.drawRect(i+50, j+50, 50, 50);
        }
    }

Answer 2

Here is the "correct" way to draw your squares.

for (int i = width; i < 400 + width; i += 100) {
    for (int j = height; j < 400 + height; j += 100) {
        g.setColor(Color.white);
        g.fillRect(i, j, 50, 50);
        g.setColor(Color.black);
        g.drawRect(i, j, 50, 50);
    }
}
for (int i = width + 50; i < 400 + width; i += 100) {
    for (int j = height + 50; j < 400 + height; j += 100) {
        g.setColor(Color.white);
        g.fillRect(i, j, 50, 50);
        g.setColor(Color.black);
        g.drawRect(i, j, 50, 50);
    }
}