新手的swing有关问题！求真理

import javax.swing.*;import java.awt.*;import java.awt.event.*;public class ShutFrame extends JFrame implements ActionListener,KeyListener{        private JLabel label_1 = null;        private JLabel label_2= null;        private JLabel overTime = null;        private JTextField HH = null;        private JTextField mm = null;        private JTextField ss = null;        private JButton exit = null;        private JButton hide = null;        private JButton start = null;    public ShutFrame(){         label_1 = new JLabel("请输入时,分,秒！");         label_2 = new JLabel("距离关机时间还有:");         overTime = new JLabel("在这里显示时间");         HH = new JTextField(3);         mm = new JTextField(3);         ss = new JTextField(3);         exit = new JButton("退出");         hide = new JButton("隐藏");         start = new JButton("开始");         JPanel jp1= new JPanel();         JPanel jp2= new JPanel();         JPanel jp3= new JPanel();         jp1.add(label_1);         jp1.add(HH);         jp1.add(mm);         jp1.add(ss);         jp2.add(label_2);         jp2.add(overTime);         jp3.add(exit);         jp3.add(hide);         jp3.add(start);         this.setLayout(new GridLayout(3,1));         this.add(jp1);         this.add(jp2);         this.add(jp3);         this.setBounds(200,200,250,200);         hide.addActionListener(this);         this.addKeyListener(this);         this.setVisible(true);    }    public void actionPerformed(ActionEvent e){        this.setVisible(false);    }    public void keyTyped(KeyEvent e){    }    public void keyPressed(KeyEvent e){        System.out.println(e.getKeyCode());        //System.out.println(e.VK_KP_DOWN);        if(e.getKeyCode() == 40){//下            }        if(e.getKeyCode() == 39){//右        }        if(e.getKeyCode() == 37){//左                }        if(e.getKeyCode() == 38){//上        }    }    public void keyReleased(KeyEvent e){        System.out.println(e.getKeyCode());    }    public static void main(String[] args){        ShutFrame s = new ShutFrame();    }    }