NullPointerException: when call "drawImage" function?

Question

hello all:
I met a java.lang.NullPointerException when I try to call drawImage in
my program.
My program structure:
1>JFrame / JPanel / ImagePane(which extends JComponent)
a object of class ImagePane stays on top of a object of JPanel which stays on JFrame.
2>code of class ImagePane
<pre>
public class ImagePane extends JComponent {
Image pic = null;
Image canvas = null;
int width = -1;
int height = -1;
public ImagePane() {
ImageIcon bird = ZoomUtil.createImageIcon("birdView.jpg");
width = bird.getIconWidth(); // ImageIcon width
height = bird.getIconHeight(); // ImageIcon height
// the image birdView.jpg is successfully loaded by java
// b/c I can get correct width and height
pic = bird.getImage();
canvas = createImage(width, height);
canvas.getGraphics().drawImage(pic, width, height, null);
// the above line get nullPointerException, when I ran program.
public void paint(Graphics g) {
g.drawImage(pic, 5, 5, 200, 250, null);
</pre>
Main program looks like:
JPanel jPanel1 = new JPanel();
ImagePane imagePaneA = new ImagePane();
jPanel1.add(imagePaneA, BorderLayout.CENTER);
thank you for any suggestion!
-Daniel

Answer 1

hello all:
I had made my code without NullPointerException, but I still cannot
get any image drawed?!
any helps are welcome!
public class ImagePane extends JComponent {
Image pic = null;
Image canvas = null;
int width = -1;
int height = -1;
public ImagePane() {
ImageIcon bird = ZoomUtil.createImageIcon("birdView.jpg");
width = bird.getIconWidth(); // ImageIcon width
height = bird.getIconHeight(); // ImageIcon height
pic = bird.getImage();
public void paint(Graphics g) {
setVisible(true);
canvas = createImage(width, height);
if (canvas == null) {
System.err.println("canvas is null"); // correct
return;
if (g.drawImage(canvas, 0, 0, this)) {
System.err.println("drawImage true"); // correct
else {
System.err.println("drawImage false");
}