代码出错，求高手指点。跪谢！ 400 请求报错 

 红色代码处报错，求高手指点。跪谢！
 
class ImagePreviewer extends JLabel {  /**   * Constructs an ImagePreviewer.   */    public ImagePreviewer(JFileChooser chooser)  {   setPreferredSize(new Dimension(100,100));   setBorder(BorderFactory.createEtchedBorder());      chooser.addPropertyChangeListener(new PropertyChangeListener()   {    public void propertyChange(PropertyChangeEvent event)    {     if(event.getPropertyName()==JFileChooser.SELECTED_FILE_CHANGED_PROPERTY)     {      //the user has selected a new file      File f=(File)event.getNewValue();      if(f==null);      {       setIcon(null);       return;      }      //read the image into an icon      ImageIcon icon = new ImageIcon (f.getPath());           //if the icon is too large to fit,scale it            if(icon.getIconWidth()>getWidth())icon=new ImageIcon(icon.getImage().getScaledInstance(getWidth(), -1, Image.SCALE_DEFAULT));         setIcon(icon);     }    }   });  } }