Java Swing - 如何get事件屏蔽Shift/控制键

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DateFormat;
import java.util.Date;
import java.util.Locale;

import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;

public class Main extends JFrame implements ActionListener {
  private JList list;
  private DefaultListModel model;

  public Main() {
    JPanel panel = new JPanel();
    panel.setLayout(null);

    model = new DefaultListModel();
    list = new JList(model);
    list.setBounds(150, 30, 220, 150);

    JButton okButton = new JButton("Ok");
    okButton.setBounds(30, 35, 80, 25);

    okButton.addActionListener(this);

    panel.add(okButton);
    panel.add(list);
    add(panel);

    setSize(420, 250);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

  }

  public void actionPerformed(ActionEvent e) {

    Locale locale = Locale.getDefault();
    Date date = new Date(e.getWhen());
    String s = DateFormat.getTimeInstance(DateFormat.SHORT, locale)
        .format(date);

    if (!model.isEmpty()) {
      model.clear();
    }

    if (e.getID() == ActionEvent.ACTION_PERFORMED) {
      model.addElement(" Event Id: ACTION_PERFORMED");

    }

    model.addElement("Time: " + s);

    String source = e.getSource().getClass().getName();

    int mod = e.getModifiers();

    StringBuffer buffer = new StringBuffer("Modifiers: ");

    if ((mod & ActionEvent.ALT_MASK) > 0) {
      buffer.append("Alt ");

    }

    if ((mod & ActionEvent.SHIFT_MASK) > 0) {
      buffer.append("Shift ");

    }

    if ((mod & ActionEvent.META_MASK) > 0) {
      buffer.append("Meta ");

    }

    if ((mod & ActionEvent.CTRL_MASK) > 0) {
      buffer.append("Ctrl ");

    }
    model.addElement(buffer);

  }

  public static void main(String[] args) {
    Main ex = new Main();
    ex.setVisible(true);
  }
}