Please Give Me Your Hands

Question

Here is my codes, I try to save the "drawing" Panel graphics into a jpg, and I can compile it, however, when I run it, system tell me" NullPointerException"!!!
I'm out of ideas, Please help, Thank you So much!!!
import java.awt.*;
import java.awt.image.*;
import javax.swing.*;
import javax.imageio.*;
import com.sun.image.codec.jpeg.*;
import java.io.*;
import java.awt.geom.*;
public class test3 extends JFrame
     public test3()
          super("test");
          setSize(800, 600);
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          drawingArea drawing = new drawingArea();
          Container c = getContentPane();
          c.add(drawing, BorderLayout.CENTER);
          int paneWidth = drawing.getWidth();
          int paneHeight = drawing.getHeight();
          BufferedImage buffer = new BufferedImage(600, 600, BufferedImage.TYPE_INT_RGB);
          buffer = (BufferedImage)drawing.createImage(paneWidth, paneHeight);
          Graphics graphic = buffer.getGraphics();
          if(graphic.getClipBounds()!=null)
               graphic.setClip(0, 0, paneWidth, paneHeight);
          drawing.paint(graphic);
          try
               File file = new File("test.jpg");
               FileOutputStream out = new FileOutputStream(file);
               JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
               JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(buffer);
          encoder.setJPEGEncodeParam(param);
          param.setQuality(1.0f,false);
               encoder.encode(buffer);
               out.flush();
               out.close();
          catch(IOException ioe)
               System.out.println(ioe.toString() + "something wrong");
          catch(RasterFormatException rfe)
               System.out.println(rfe.toString() + "rfe");
          setVisible(true);
     class drawingArea extends JPanel
          public void paintComponent(Graphics g)
               Graphics2D g2D = (Graphics2D)g;
               Rectangle2D.Float rect = new Rectangle2D.Float(50F, 50F, 20F, 20F);
               g2D.draw(rect);
     public static void main(String args[])
          test3 t = new test3();
}

Answer 1

1 - the graphics context of a Component is null until the Component is realized, ie, until you call pack or setVisible on its top-level Container
2 - you can make up a BufferedImage and save it without using a Component to show it
3 - using a 'png' extension seems to give better results and a smaller file size than 'jpg'
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.*;
import javax.imageio.ImageIO;
import javax.swing.*;
public class ImageTest
    ImageTestPanel imagePanel;
    ImageTestUtility utility;
    BufferedImage image;
    public ImageTest()
        createImage();
        imagePanel = new ImageTestPanel();
        utility = new ImageTestUtility();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(getUIPanel(), "North");
        f.getContentPane().add(imagePanel);
        f.setSize(400,400);
        f.setLocation(200,200);
        System.out.println("imagePanel graphics context before visible = " +
                            imagePanel.getGraphics());
        f.setVisible(true);
        System.out.println("imagePanel graphics context after realized = " +
                            imagePanel.getGraphics());
    private void createImage()
        int w = 200;
        int h = 200;
        image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = image.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.white);
        g2.fillRect(0, 0, w, h);
        g2.setPaint(Color.blue);
        g2.draw(new Rectangle2D.Double(w/16, h/16, w*7/8, h*7/8));
        int dia = Math.min(w, h)/4;
        g2.setPaint(Color.red);
        g2.draw(new Ellipse2D.Double(w/2 - dia/2, h/2 - dia/2, dia, dia));
        g2.setPaint(Color.green.darker());
        g2.draw(new Line2D.Double(w/16, h*15/16, w*15/16, h/16));
        g2.dispose();
    private JPanel getUIPanel()
        final JButton
            saveComponent = new JButton("save component"),
            saveImage = new JButton("save image");
        ActionListener l = new ActionListener()
            public void actionPerformed(ActionEvent e)
                JButton button = (JButton)e.getSource();
                if(button == saveComponent)
                    utility.saveComponent(imagePanel);
                if(button == saveImage)
                    utility.saveToFile(image);
        saveComponent.addActionListener(l);
        saveImage.addActionListener(l);
        JPanel panel = new JPanel();
        panel.add(saveComponent);
        panel.add(saveImage);
        return panel;
    public static void main(String[] args)
       new ImageTest();
class ImageTestPanel extends JPanel
    public ImageTestPanel() { }
    protected void paintComponent(Graphics g)
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.red);
        g2.draw(new Rectangle2D.Float(50, 50, 20, 20));
class ImageTestUtility
    public BufferedImage loadImage(String fileName)
        BufferedImage image = null;
        try
            URL url = getClass().getResource(fileName);
            image = ImageIO.read(url);
        catch(MalformedURLException mue)
            System.err.println("url: " + mue.getMessage());
        catch(IOException ioe)
            System.err.println("read: " + ioe.getMessage());
        return image;
    public void saveComponent(Component c)
        int w = c.getWidth();
        int h = c.getHeight();
        BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = bi.createGraphics();
        c.paint(g2);
        g2.dispose();
        saveToFile(bi);
    public void saveToFile(BufferedImage image)
        try
            ImageIO.write(image, "jpg", new File("imageTest.jpg"));
        catch(IOException ioe)
            System.err.println("write: " + ioe.getMessage());
}