Java keyListener multi touche

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.TreeSet;

import javax.swing.JFrame;
import javax.swing.JLabel;

class MultipleListener implements KeyListener
{
    private TreeSet<Integer> set = new TreeSet<Integer>();
    private final JLabel label;
    private final String EMPTY = "Press Any Key";
    
    public MultipleListener()
    {
        System.out.println(set);
        label = new JLabel(EMPTY,JLabel.CENTER);
    }
    
    public JLabel getLabel()
    {
        return label;
    }
    
    @Override
    public void keyPressed(KeyEvent e) 
    {
        if (set.add(e.getExtendedKeyCode()))
        {
            System.out.println(set);
            label.setText(set.toString());
        }
    }
    
    @Override
    public void keyReleased(KeyEvent e)
    {
        if(set.remove(e.getExtendedKeyCode()))
        {
            System.out.println(set);
            if (set.isEmpty())
                label.setText(EMPTY);
            else
                label.setText(set.toString());
        }
    }
    
    @Override
    public void keyTyped(KeyEvent e)
    {
    }
}

public class Test
{    
    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setSize(200,100);
                        
        MultipleListener listener = new MultipleListener();
        frame.add(listener.getLabel());
        frame.addKeyListener(listener);
        
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}