Unable to draw a simple image using JComponent

I'm using netbeans IDE to pr开发者_如何学编程actice some Java basic code. But I'm unsuccessful to draw a PNG image. Below is my code,

package JavaApplication1;

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

class MyCanvas extends JComponent
{
    Image img;
    public MyCanvas(){
        img = Toolkit.getDefaultToolkit().createImage("pengbrew.png");
    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(img, 0, 0, null);
    }
}

public class JavaGame
{
    public static void main(String args[]){
        JFrame window = new JFrame("Image demo");
        window.getContentPane().add( new MyCanvas() );
        window.setSize(400,400);
        window.setVisible(true);
    }
}

I added the images in the netbeans project.

Please advise.

Many thanks.

easiest ways is look for JLabel that's best of JComponents for Icon/ImageIcon examples here

To load an image use ImageIO.read(File file). It's a newer API, easier to use and better supported. A tutorial on loading images is here http://docs.oracle.com/javase/tutorial/2d/images/loadimage.html if you need some more pointers.

Your code would look like this instead,

Image img;
public MyCanvas(){
    try {
        img = ImageIO.read(new File("pengbrew.png"));
    } catch (IOException e) {
        // Handle exception if there is one.
    }
}

For the long answer about why the method you were using wasn't working is probably because of the following...

Your image may be in the proper location and instead Toolkit.createImage() hasn't finished loading the image before the frame comes up to paint. Toolkit.createImage() returns control back to your application before the underlying image has actually finished being loaded. You can usually verify if this is the issue by resizing your application to force it to repaint. If after a few seconds of trying to resize the application the image shows up it was due to the image not being loaded during the first paint calls.

To ensure that the image is loaded before you continue you need to use a MediaTracker. Here is some example code to ensure loading of Image is complete before using it.

Component component = new Component() {};
MediaTracker TRACKER = new MediaTracker(component);

...

Image image = Toolkit.getDefaultToolkit().createImage("imageToLoad.png");
synchronized(TRACKER) {
   int id = ++mediaTrackerID;
   TRACKER.addImage(image, id);
   try {
       TRACKER.waitForID(id, 0);
   } catch (InterruptedException ex) {
       image = null;
   }
   TRACKER.removeImage(image, id);
}
// Now you can use your image.

You'll see code just like this in the ImageIcon class in the method loadImage(Image image).