请教一个swing问题

Question

如果图象没有装载完毕，那就可能显示空白。

Answer 1

怎么能判断图像没有装载完毕？

Answer 2

给试试这样做，在我机器上测试通过的：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.beans.*;
import java.io.*;public class Test extends JFrame {
  JFileChooser chooser = new JFileChooser();
  ImagePreviewer previewer = new ImagePreviewer();  public Test() {
    super("Accessory Components");    Container contentPane = getContentPane();
    JButton button = new JButton("Select A File");    contentPane.setLayout(new FlowLayout());
    contentPane.add(button);    setAccessoryComponent();    button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        chooser.showOpenDialog(null);
      }
    });
  }  private void setAccessoryComponent() {
    JPanel previewPanel = new JPanel();    previewPanel.setLayout(new BorderLayout());
    previewPanel.add(new JLabel("Image Previewer",
                                SwingConstants.CENTER),
                     BorderLayout.NORTH);    previewPanel.add(previewer, BorderLayout.CENTER);    previewer.setPreferredSize(new Dimension(200, 0));
    previewer.setBorder(BorderFactory.createEtchedBorder());    chooser.setAccessory(previewPanel);    new ImagePreviewerAccessoryAdapter(chooser, previewer);
  }  public static void main(String a[]) {
    JFrame f = new Test();
    f.setBounds(300, 300, 300, 75);
    f.setVisible(true);    f.addWindowListener(new WindowAdapter() {
      public void windowClosed(WindowEvent e) {
        System.exit(0);
      }
    });
  }
}class ImagePreviewerAccessoryAdapter {
  public ImagePreviewerAccessoryAdapter(
      JFileChooser chooser,
      final ImagePreviewer previewer) {
    chooser.addPropertyChangeListener(new PropertyChangeListener() {
      public void propertyChange(PropertyChangeEvent e) {
        if (e.getPropertyName().equals(JFileChooser.SELECTED_FILE_CHANGED_PROPERTY)) {
          if(e.getNewValue() != null)
            previewer.update((File)e.getNewValue());
        }
      }
    });
  }
}class ImagePreviewer extends JComponent {
  private ImageIcon icon;  public void update(File file) {
    Dimension size = getSize();
    Insets insets = getInsets();    icon = new ImageIcon(file.getPath());    icon.setImage(icon.getImage().getScaledInstance(
        size.width - insets.left - insets.right,
        size.height - insets.top - insets.bottom,
        Image.SCALE_SMOOTH));    if (isShowing()) {
      repaint();
    }
  }  public void paintComponent(Graphics g) {
    Insets insets = getInsets();    super.paintComponent(g);    if (icon != null)
      icon.paintIcon(this, g, insets.left, insets.top);
  }
}