Java Swing - 如何添加JCheckBox组件到JComboBox

import java.awt.Color;
import java.awt.Component;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;

public class Main {
  public static void main(String[] args) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getContentPane().add(new CheckCombo().getContent());
    f.setSize(300, 160);
    f.setLocation(200, 200);
    f.setVisible(true);
  }
}

class CheckCombo implements ActionListener {
  public void actionPerformed(ActionEvent e) {
    JComboBox cb = (JComboBox) e.getSource();
    CheckComboStore store = (CheckComboStore) cb.getSelectedItem();
    CheckComboRenderer ccr = (CheckComboRenderer) cb.getRenderer();
    ccr.checkBox.setSelected((store.state = !store.state));
  }

  public JPanel getContent() {
    String[] ids = { "north", "west", "south", "east" };
    Boolean[] values = { Boolean.TRUE, Boolean.FALSE, Boolean.FALSE,
        Boolean.FALSE };
    CheckComboStore[] stores = new CheckComboStore[ids.length];
    for (int j = 0; j < ids.length; j++)
      stores[j] = new CheckComboStore(ids[j], values[j]);
    JComboBox combo = new JComboBox(stores);
    combo.setRenderer(new CheckComboRenderer());
    combo.addActionListener(this);
    JPanel panel = new JPanel();
    panel.add(combo);
    return panel;
  }
}

class CheckComboRenderer implements ListCellRenderer {
  JCheckBox checkBox;

  public CheckComboRenderer() {
    checkBox = new JCheckBox();
  }

  public Component getListCellRendererComponent(JList list, Object value,
      int index, boolean isSelected, boolean cellHasFocus) {
    CheckComboStore store = (CheckComboStore) value;
    checkBox.setText(store.id);
    checkBox.setSelected(((Boolean) store.state).booleanValue());
    checkBox.setBackground(isSelected ? Color.red : Color.white);
    checkBox.setForeground(isSelected ? Color.white : Color.black);
    return checkBox;
  }
}

class CheckComboStore {
  String id;
  Boolean state;

  public CheckComboStore(String id, Boolean state) {
    this.id = id;
    this.state = state;
  }
}