applet显示问题

Question

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class PanelTest extends JApplet
{
  JPanel panelobj = null;
  public PanelTest()
  {
    panelobj=new JPanel();
    getContentPane().add(panelobj);
  }
}
class ButtonTest extends PanelTest
{
   JButton button1,button2;
   JTextField textobj;
   public ButtonTest()
   {
     button1=new JButton("录入");
     button2=new JButton("消除");
     textobj=new JTextField("",20);
     panelobj.add(button1);
     panelobj.add(button2);
     panelobj.add(textobj);
   }
}
class GridBagTest extends ButtonTest
{
  GridBagLayout layoutobj;
  GridBagConstraints gbcobj;
  public GridBagTest()
  {
    layoutobj=new GridBagLayout();
    gbcobj=new GridBagConstraints();
    gbcobj.gridx=1; 
    gbcobj.gridy=1;
    gbcobj.gridwidth=2;
    layoutobj.setConstraints(textobj,gbcobj);  
    gbcobj.gridy=2;
    gbcobj.gridwidth=1;
    layoutobj.setConstraints(button1,gbcobj);        
    gbcobj.gridx=2;
    layoutobj.setConstraints(button2,gbcobj);   
  }
}
class EventTest  extends GridBagTest
{
  ButtonEvent beobj;
  public EventTest()
  {
    beobj=new ButtonEvent();
    button1.addActionListener(beobj);
    button2.addActionListener(beobj);
  }
  class ButtonEvent implements ActionListener
  {
    public void actionPerformed(ActionEvent e)
    {
      Object obj=e.getSource();
      if(obj==button1)
      {
        String strobj=textobj.getText();
        if(strobj.length()==0) 
        {
          getAppletContext().showStatus("警告! 文本框不能为空");
          return;
        }
        else
        {
          getAppletContext().showStatus("文本内容是: "+strobj);
          button1.setEnabled(false);  
          button2.setEnabled(true);  
        }
      }
      if(obj==button2)
      {
        button1.setEnabled(true); 
        button2.setEnabled(false); 
        textobj.setText("");
        getAppletContext().showStatus("文本内容清空");
      }
    }
  }
}
public class StatusTest
{
 public void init()
 {
    new EventTest();
 }
}
错误信息:
F:\StatusTest>javac StatusTest.javaF:\StatusTest>appletviewer StatusTest.html
java.lang.ClassCastException: StatusTest
        at sun.applet.AppletPanel.createApplet(AppletPanel.java:712)
        at sun.applet.AppletPanel.runLoader(AppletPanel.java:641)
        at sun.applet.AppletPanel.run(AppletPanel.java:320)
        at java.lang.Thread.run(Thread.java:595)

Answer 1

public class StatusTest
{
 public void init()
 {
    new EventTest();
 }
}没有继承applet类