Question

As the title says, I’m having a hard time trying to draw some rectangles (filled) in JApplet.
The exact goal is to have a 50×50 table and when you click on a targeted cell, to make it filled (possibly done by drawing a filled rectangle). I have done the maths about the coordinates of the starting point, but for some reason I can’t draw the new rectangle in the MouseClicked method. Any suggestions?

public class Main extends JApplet {

public static final int DIMX = 800;
public static final int DIMY = 800;
public static final int ratio = 16;
Graphics g;
boolean drawing;
public int cX;
public int cY;

public Main() {
    JPanel MainFrame = new JPanel();
    MainFrame.setPreferredSize(new Dimension(400, 800));
    MainFrame.setBackground(Color.LIGHT_GRAY);
    JPanel Table = new JPanel();
    Table.setPreferredSize(new Dimension(800, 800));
    Table.setBackground(Color.LIGHT_GRAY);
    add(MainFrame, BorderLayout.EAST);
    add(Table, BorderLayout.WEST);
    addMouseListener(new clicked());
}



public void paint(Graphics g) {
    super.paintComponents(g);
    g.setColor(Color.black);
    for (int i = 0; i <= 800; i += 16) {
        g.drawLine(0, i, 800, i);
        g.drawLine(i, 0, i, 800);
//            g.fillRect(cX, cY, 16, 16);
    }
}

public static void main(String[] args) {
    JFrame win = new JFrame("Retarded Bullshit");
    win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    win.setPreferredSize(new Dimension(1216, 840));
    win.setContentPane(new Main());
    win.pack();
    win.setVisible(true);

}

public class clicked extends JApplet implements MouseListener {

public int cX;
public int cY;
Graphics g;

@Override
public void mouseClicked(MouseEvent e) {
//            Point a = e.getLocationOnScreen();
    int cellX = e.getX();
    int cellY = e.getY();
    if (cellX < 800 && cellX > 0 && cellY < 800 && cellY > 0) {
        cX = cellX / 16 + 1;
        cY = cellY / 16 + 1;

        JOptionPane.showMessageDialog(null, "" + cX + " " + cY);
    }

Answer 1

This is a relatively simple concept (no offense).

To start with, don’t mix your code with JApplet and JFrame. If you want to use your application in these two mediums, separate the logic into a separate component (like JPanel) which you can easily add to either. You really shouldn’t add a top level container to another top level container (adding an applet to a frame) – it’s messy.

Avoid overriding the paint methods of top level containers (like JApplet), instead, use a custom component (like JPanel) instead and override it’s paintComponent method.

In your example, you should be calling super.paint rather then super.paintComponents. paint does important work, you don’t want to skip it – but you should be using JComponent#paintComponent

MouseListeners should added to the components that you are interested in managing mouse events. Because clicked is never added to any containers, it will never recieve mouse events.

Take a look at

• How to write mouse listeners
• Performing Custom Painting
• 2D Graphics
• Painting in AWT and Swing (because every Swing developer should have an understanding of this)

public class SimplePaint03 {

    public static void main(String[] args) {
        new SimplePaint03();
    }

    public SimplePaint03() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new PaintPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class PaintPane extends JPanel {

        private List<Shape> grid;
        private List<Shape> fill;

        public PaintPane() {
            grid = new ArrayList<>(5);
            fill = new ArrayList<>(5);
            addMouseListener(new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {
                    for (Shape shape : grid) {
                        if (shape.contains(e.getPoint())) {
                            if (fill.contains(shape)) {
                                fill.remove(shape);
                            } else {
                                fill.add(shape);
                            }
                        }
                    }
                    repaint();
                }
            });

            int colWidth = 200 / 50;
            int rowHeight = 200 / 50;

            for (int row = 0; row < 50; row++) {
                for (int col = 0; col < 50; col++) {
                    grid.add(new Rectangle(colWidth * col, rowHeight * row, colWidth, rowHeight));
                }
            }

        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g); 
            Graphics2D g2d = (Graphics2D) g;
            g2d.setColor(Color.RED);
            for (Shape cell : fill) {
                g2d.fill(cell);
            }
            g2d.setColor(Color.BLACK);
            for (Shape cell : grid) {
                g2d.draw(cell);
            }
        }

    }

}

Additional

Information from one paint cycle to another is not maintained. You are required to repaint the component exactly the way you want it to appear. This means you will need to maintain a list of click points that can be repainted at any time.