Java Swing - 如何控件字体与JCheckBox ActionListener

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Main {
  public static void main(String[] args) {
    CheckBoxFrame frame = new CheckBoxFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }
}

class CheckBoxFrame extends JFrame {
  int DEFAULT_WIDTH = 300;
  int DEFAULT_HEIGHT = 200;

  private JLabel label;
  private JCheckBox bold;
  private JCheckBox italic;

  private static final int FONTSIZE = 12;
  public CheckBoxFrame() {
    setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    label = new JLabel("The quick brown fox jumps over the lazy dog.");
    label.setFont(new Font("Serif", Font.PLAIN, FONTSIZE));
    add(label, BorderLayout.CENTER);

    ActionListener listener = new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        int mode = 0;
        if (bold.isSelected())
          mode += Font.BOLD;
        if (italic.isSelected())
          mode += Font.ITALIC;
        label.setFont(new Font("Serif", mode, FONTSIZE));
      }
    };

    JPanel buttonPanel = new JPanel();

    bold = new JCheckBox("Bold");
    bold.addActionListener(listener);
    buttonPanel.add(bold);

    italic = new JCheckBox("Italic");
    italic.addActionListener(listener);
    buttonPanel.add(italic);

    add(buttonPanel, BorderLayout.SOUTH);
  }
}