paint() method would not draw on JPanel

Question

I tried few source codes of drawing in java and they were working fine, but when i tried to make one of my own I could not get the paint(Grahpics g) method to work! I looked again at the codes I have and checked some of the tutorials in Oracle's pages but i don't seem to be able to know why it would not work. can someone please check it and tell me what is wrong here??

main method: public class main

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

board:

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;


public class board implements ActionListener
{
    private JFrame f = new JFrame("Speedy");
    private JPanel gamePanel = new JPanel();


    private Image bg = new ImageIcon(this.getClass().getResource("road.png")).getImage();
    private Timer t;


    private car myCar = new car();


    public board()
    {
        t = new Timer(50,this);
        t.start();


        gamePanel.setSize(600,400);
        gamePanel.setDoubleBuffered(true);
        gamePanel.setFocusable(true);
        gamePanel.addKeyListener(new TAdapter());

        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(gamePanel,BorderLayout.CENTER);
        //f.addKeyListener(new TAdapter());
        f.setBounds(200,100,600,400);
        f.setVisible(true);
        f.revalidate();
        f.repaint();

    }




    public void paint(Graphics g) {
        gamePanel.paint(g);

        Graphics2D g2d = (Graphics2D)g;
        g2d.drawImage(bg,0,0,null);
        g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

        System.out.println("Painted");

        g.dispose();
    }



    public void actionPerformed(ActionEvent e) 
    {
        gamePanel.repaint();
        //System.out.println("Painting..");
    }





    private class TAdapter extends KeyAdapter {

        public void keyReleased(KeyEvent e) {}

        public void keyPressed(KeyEvent e)  
        {
            myCar.keyPressed(e);
            System.out.println("You pressed: "+e);
        }
    }

}

car.java:

    import java.awt.Image;
    import java.awt.event.KeyEvent;
    import java.util.ArrayList;

    import javax.swing.ImageIcon

;



public class car 
{

    private Image image;
    public int xPos,yPos;

    public car()
    {
        image = new ImageIcon(this.getClass().getResource("car.png")).getImage();
        xPos = 300;
        yPos = 200;
        System.out.println(image.getWidth(null));
    }



    public Image getImg() {return image;}


    public void move() {}


    public void keyPressed(KeyEvent e) 
    {

        int key = e.getKeyCode();

        if (key == KeyEvent.VK_LEFT) xPos -= 1;
        if (key == KeyEvent.VK_RIGHT)xPos += 1;
        if (key == KeyEvent.VK_UP)   yPos -= 1;
        if (key == KeyEvent.VK_DOWN) yPos += 1;
    }

}

There are no errors, it shows me the width of the image which is right, also the timer triggers the ActionListener, also KeyListener is working, but the images would not draw! the paint(Graphics g) method just does not want to get triggered! Googling it did not help.. I thought this would be a common problem but nobody has the problem I have, all solutions failed me. help please? If someone can explain it would be most appreciated!

Answer 1

Your class Board does not extend the JPanel class. So the paint() method is never called by the Swing. Also, the statement gamePanel.repaint() will only execute the default JPanel paint() method of gamePanel. Instead you want the overridden paint method to be executed, so might want to do this:

public class Board extends JPanel implements ActionListener {
   ....
    public void paint(Graphics g) {
       this.paint(g);

       Graphics2D g2d = (Graphics2D)g;
       g2d.drawImage(bg,0,0,null);
       g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

       System.out.println("Painted");

       g2d.dispose();
    }
    ....
}

Replace your action functionality with this:

public void actionPerformed(ActionEvent e) {
   this.repaint();
}

Alternative solution: If you do not want your Board class to extend JPanel, you can also override the paint() method of the gamePanel as you initialize it.

gamePanel = new JPanel() {
   @Override
   public void paint(Graphics g) {
       this.paint(g);

       Graphics2D g2d = (Graphics2D)g;
       g2d.drawImage(bg,0,0,null);
       g2d.drawImage(myCar.getImg(), myCar.xPos, myCar.yPos, null);

       g2d.dispose();
   }
};

However, I would recommend the first solution rather than this one with anonymous classes.