CreateImage Applet/JFrame

Question

Hi, i got this problem with the createImage method, what i am trying to do is to create several smaller images from a larger image, the program works perfectly in an Applet but if i change this line:
public class ImgBDemo extends Applet {To:
public class ImgBDemo extends JFrame {I get a NullPointerException at this line:
upImage = imgBDemo.createImage(w, h);
g = upImage.getGraphics(); //HERE I GET THE NullPointerException
g.drawImage(bigimage, -col*w, -row*h, imgBDemo);Could anyone please tell me what the problem is and if there is any way to fix this problem.
Thx.
Here is the code, it's not stand-alone so it won't work if you try to run it.
import java.applet.Applet;
import java.awt.Color;
import java.awt.Event;
import java.awt.Graphics;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.Toolkit;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ImgBDemo extends Applet {
     boolean showImageLoadingStatus = true;
     public Image getImageNow(String imagePath) {
          MediaTracker tracker = new MediaTracker(this);
          Image image = null;
          if (showImageLoadingStatus) {
               System.out.println("Loading image: " + imagePath);
          image = Toolkit.getDefaultToolkit().getImage(imagePath);
          tracker.addImage(image, 0);
          try {
               image = Toolkit.getDefaultToolkit().getImage(imagePath);
               tracker.addImage(image, 0);
               tracker.waitForID(0);
          catch (InterruptedException e) {
          if (tracker.isErrorID(0)) {
               System.out.println("ERROR loading image: " + imagePath);
               System.out.println("ERROR loading image: " + imagePath);
          if (showImageLoadingStatus) {
               System.out.println("");
          return image;
     public void init() {
          ControlPanel cp = new ControlPanel(this);
          add(cp);
     public static void main(String args[]) {
          JFrame f = new JFrame("Kali");
          ImgBDemo imgBDemo = new ImgBDemo();
          imgBDemo.init();
          f.add("Center", imgBDemo);
          f.setSize(300, 300);
          f.setVisible(true);
class ControlPanel extends JPanel {
     ImgBDemo imgBDemo;
     ImageButton[] groupButton = new ImageButton[36];
     ImageButton[] colorButton = new ImageButton[6];
     GridBagLayout gridbag = new GridBagLayout();
      * Create a new control panel object.
     public ControlPanel(ImgBDemo imgBDemo) {
          this.imgBDemo = imgBDemo;
          setBackground(Color.lightGray);
          int buttonRowCount = 7;
          int buttonsPerRow = 6;
          Image bigimage = imgBDemo.getImageNow("buttons.png");
          Image upImage, downImage;
          int w = 32, h = 32;
          Graphics g;
          int row = 0;
          int col = 0;
          GridBagConstraints c;
          setLayout(gridbag);
          //   Create the group buttons; each button gets put into
          //   its own little panel (the bPanel array) together with
          //   its label.  It's in this loop where we chop up the big
          //   image into individual ones for the buttons.
          ImageButtonGroup groupButtons = new ImageButtonGroup();
          JPanel[] bPanel = new JPanel[groupButton.length];
          c = new GridBagConstraints();
          c.gridwidth = GridBagConstraints.REMAINDER;
          for (int i=0; i<36; ++i) {
               upImage = imgBDemo.createImage(w, h);
                * Here is where i get the null pointer exception, the previous createImage(w,h)
                * only seems to return null when using JFrame, in an Applet it works fine.
               g = upImage.getGraphics();
               g.drawImage(bigimage, -col*w, -row*h, imgBDemo);
               downImage = imgBDemo.createImage(w, h);
               g = downImage.getGraphics();
               g.drawImage(bigimage, -col*w, -(row+buttonRowCount)*h, imgBDemo);
               groupButton[i] = new ImageButton(upImage, downImage, groupButtons);
               bPanel[i] = new JPanel();
               bPanel.setLayout(gridbag);
               gridbag.setConstraints(groupButton[i], c);
               bPanel[i].add(groupButton[i]);
               ++col;
               if (col >= buttonsPerRow) {
                    col = 0;
                    ++row;
          // Create the color buttons
          ImageButtonGroup colorButtons = new ImageButtonGroup();
          for (int i=0; i<6; ++i) {
               upImage = imgBDemo.createImage(w, h);
               g = upImage.getGraphics();
               g.drawImage(bigimage, -col*w, -row*h, imgBDemo);
               downImage = imgBDemo.createImage(w, h);
               g = downImage.getGraphics();
               g.drawImage(bigimage, -col*w, -(row+buttonRowCount)*h, imgBDemo);
               colorButton[i] = new ImageButton(upImage, downImage, colorButtons);
               ++col;
               if (col >= buttonsPerRow) {
                    col = 0;
                    ++row;
          // Create the color panel and layout the color
          // buttons in it.
          JPanel colorPanel = new JPanel();
               colorPanel.setLayout(new GridLayout(1,6));
               for (int i=0; i<6; ++i) {
                    colorPanel.add(colorButton[i]);
          // color panel
          gridbag.setConstraints(colorPanel, c);
          add(colorPanel);
     * Given a color button, return its index.
     public int findColor(ImageButton button) {
          return -1;
     * Handling method for button actions.
     public boolean action(Event e, Object arg) {
          if (e.target instanceof ImageButton) {
               ImageButton button = (ImageButton)e.target;
               int i = findColor(button);
               if (i>=0) {
//                    currentColor = i;
               } else {
                    System.out.println("unknown image button pressed");
          return true;

Answer 1

So the trick is simply to display the containers before i create the image, got it.
Thx.