Why the painted content flash and disappear?

Question

I try to run a simple code example from java almanac site but the painted content just flash and disappear. Can any people help to find the reason? Thanks in advance.
Below are the code:
package font;
import java.text.AttributedString;
import java.awt.*;
import java.awt.font.LineBreakMeasurer;
import java.awt.font.TextLayout;
import javax.swing.*;
public class DrawParagraphDemo extends JPanel {
    public DrawParagraphDemo() {
        this.setPreferredSize(new Dimension(500,500));
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
        //Create and set up the window.
        JFrame frame = new JFrame("Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Create and set up the content pane.
        DrawParagraphDemo demo = new DrawParagraphDemo();
        frame.setContentPane(demo);
        //Display the window.
        frame.pack();
        frame.setVisible(true);
        demo.drawParagraph((Graphics2D) demo.getGraphics(), "One line of test string", 400);
    public void drawParagraph(Graphics2D g, String paragraph, float width) {
        LineBreakMeasurer linebreaker = new LineBreakMeasurer(
            new AttributedString(paragraph).getIterator(), g.getFontRenderContext());
        float y = 0.0f;
        while (linebreaker.getPosition() < paragraph.length()) {
            TextLayout tl = linebreaker.nextLayout(width);
            System.out.println(tl);
            y += tl.getAscent();
            tl.draw(g, 0, y);
            y += tl.getDescent() + tl.getLeading();
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
}

Answer 1

Hi i have similar problem and i have followed Camickr's suggestion but it looks like my image was still being painted over here's my code
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.filechooser.*;
* FileChooserDemo2.java is a 1.4 application that requires these files:
*   ImageFileView.java
*   ImageFilter.java
*   ImagePreview.java
*   Utils.java
*   images/jpgIcon.gif (required by ImageFileView.java)
*   images/gifIcon.gif (required by ImageFileView.java)
*   images/tiffIcon.gif (required by ImageFileView.java)
*   images/pngIcon.png (required by ImageFileView.java)
public class Asst4 extends JPanel
                              implements ActionListener {
    static private String newline = "\n";
    private JTextArea log;
    private JFileChooser fc;
     private JPanel display,button;
     JButton load,grey,color;
     private Image image;
     static JComponent newContentPane;
    public Asst4() {
        super(new BorderLayout());
        //Create the log first, because the action listener
        //needs to refer to it.
          display=new JPanel();
          display.setOpaque(true);
          button=new JPanel();
          load=new JButton("Load Image");
          grey=new JButton("Greyscale Image");
          color=new JButton("Color Image");
          load.addActionListener(this);
          //display.setBackground(Color.BLACK);
          //System.out.println("displayable: "+isDisplayable()+" visible: "+isVisible()+" valid: "+isValid());
          //System.out.println("displayable: "+display.isDisplayable()+" visible: "+display.isVisible()+" valid: "+display.isValid());
          display.setSize(500,500);
          button.add(load, BorderLayout.WEST);
          button.add(grey, BorderLayout.CENTER);
          button.add(color, BorderLayout.EAST);
          add(button,BorderLayout.NORTH);
          add(display,BorderLayout.CENTER);
          setVisible(true);
    public void actionPerformed(ActionEvent e) {
               //Set up the file chooser.
               if (fc == null) {
                    fc = new JFileChooser();
                    //Add a custom file filter and disable the default
                    //(Accept All) file filter.
                    fc.addChoosableFileFilter(new ImageFilter());
                    fc.setAcceptAllFileFilterUsed(false);
                    //Add custom icons for file types.
                    fc.setFileView(new ImageFileView());
                    //Add the preview pane.
                    fc.setAccessory(new ImagePreview(fc));
                    //Show it.
               int returnVal = fc.showDialog(Asst4.this,"Load Image");
               //Process the results.
               if (returnVal == JFileChooser.APPROVE_OPTION) {
                    File file = fc.getSelectedFile();
                    Toolkit toolkit = Toolkit.getDefaultToolkit();
                    image = toolkit.getImage(file.getAbsolutePath());
                    MediaTracker mediaTracker = new MediaTracker(this);
                    mediaTracker.addImage(image,0);
                    try {
                       mediaTracker.waitForID(0);
                    } catch (InterruptedException ie) {
                       System.err.println(ie);
                       System.exit(1);
               } else {
                    System.out.println("Loading cancelled by user." );
               fc.setSelectedFile(null);
    protected void paintComponent(Graphics g)
          super.paintComponent(g); // this paints the background
          if(image!=null)
          drawImage(image);
    private void drawImage(Image image){
          Graphics2D g=(Graphics2D)display.getGraphics();
          g.drawImage(image,0,0,null);
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
        JDialog.setDefaultLookAndFeelDecorated(true);
        //Create and set up the window.
        JFrame frame = new JFrame("Compsci_375_Assignment_4");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Create and set up the content pane.
        newContentPane = new Asst4();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        //Display the window.
        frame.setBounds(50,50,500,500);
           //frame.pack();
        frame.setVisible(true);
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
}Can anyone tell me what's going on and also why if i pack the frame my display panel is disappear?
Thanks a lot