Question

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class Main
{
    JFrame jf;
    Main()
    {
        jf=new JFrame();
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.add(new MyCanvas());
        jf.pack();
        jf.setVisible(true);
    }
    public static void main(String[] args)
    {
        MyCanvas.img=Toolkit.getDefaultToolkit().createImage("1.jpg");
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                new Main();
            }
        });
    }
}
class MyCanvas extends JComponent
{
    static Image img;
    BufferedImage bi;
    MyCanvas()
    {
        setPreferredSize(new Dimension(200,200));
        bi=new BufferedImage(200,200,BufferedImage.TYPE_INT_ARGB);
        Graphics g=bi.getGraphics();
        for (int i=0;i<10;i++)
            for (int j=0;j<10;j++)
                g.drawImage(img,i*20,j*20,20,20,this);
    }
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.drawImage(bi,0,0,this);
        //g.drawImage(img,0,0,this);
    }
}

If I uncomment line g.drawImage(img,0,0,this); I get my image on window. But with this code I see empty window. It is easy to understand that g.drawImage(img,i*20,j*20,20,20,this); in loop doesn’t draw but what is problem?

Answer 1

edited out the unrelated stuff I did for future readers to find the answer easier. In java i’ve always had to use getResource or getResourceAsStream to ensure the file loaded from the right directory correctly.

class MyCanvas extends JComponent
{
    public static Image loadImage(String s)
    {
        try 
        {
            return ImageIO.read(Main.class.getResource(s));
        } 
        catch (Exception ex) 
        {
            ex.printStackTrace();
            return null;
        }
    }
}