问没有Main函数

EN

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;

public class StyleListener extends JPanel
{
private static final long serialVersionUID = 1L;
private JCheckBox bold, italic;
private JLabel saying;
private JSplitPane splitPane;

public StyleListener()

 {  
   splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT);
   splitPane.setOneTouchExpandable(true);
   splitPane.setPreferredSize(new Dimension(300,200));
   splitPane.setBackground(Color.green);
   splitPane.setDividerLocation(100);

   JPanel subPanel1 = new JPanel();
   subPanel1.setPreferredSize(new Dimension(300, 100));
   subPanel1.setBackground(Color.cyan);
   saying = new JLabel ("Say it with style!");
   saying.setFont (new Font ("Helvetica", Font.PLAIN, 36));
   subPanel1.add (saying);
   splitPane.setTopComponent(subPanel1);

   JPanel subPanel2 = new JPanel();
   subPanel2.setPreferredSize(new Dimension(300, 100));
   subPanel2.setBackground(Color.green);
   bold = new JCheckBox ("Bold");
   bold.setToolTipText("Check this box to make text fatter.");
   bold.setBackground (Color.green);
   italic = new JCheckBox ("Italic");
   italic.setToolTipText("Check this box to make text slantier looking.");
   italic.setBackground (Color.green);
   subPanel2.add (bold);
   subPanel2.add (italic);
   splitPane.setBottomComponent(subPanel2);

   add(splitPane);

   StyleListener listener = new StyleListener();
   bold.addItemListener (listener);
   italic.addItemListener (listener);

   public void itemStateChanged (ItemEvent event)
   {
      int style = Font.PLAIN;

      if (bold.isSelected())
        style = Font.BOLD;

      if (italic.isSelected())
        style += Font.ITALIC;

      saying.setFont (new Font ("Helvetica", style, 36));
   }