java中给键盘添加了侦听却没有实现，这是为什么啊？

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class Animation extends JFrame implements Runnable,ActionListener,KeyListener{
private Container cont;
private JButton btnUp;
private JButton btnDown;
private ImageIcon imgPlane;
private ImageIcon imgBullet;
private int planeX;
private int planeY;
private int bulletX;
private int bulletY;
private int planeSpeed;
private int bulletSpeed;
private int planeChangeSpeed;
private Thread thread;
public Animation(){
addKeyListener(this);
this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
GameStartInit();
}
public void GameStartInit(){
cont =this.getContentPane();
this.setBounds(0,0,400,300);
cont.setLayout(null);
imgPlane = new ImageIcon("plane.gif");
imgBullet = new ImageIcon("bullet.gif");
planeX = 0;
planeY = 150;
bulletX = 400;
bulletY = 150;
planeSpeed = 8;
bulletSpeed = 8;
planeChangeSpeed = 6;
btnUp = new JButton("up");
btnDown = new JButton("down");
btnUp.setBounds(0, 240, 80, 30);
btnDown.setBounds(90, 240, 80, 30);
btnUp.addActionListener(this);
btnDown.addActionListener(this);
cont.add(btnUp);
cont.add(btnDown);
thread = new Thread(this);
thread.start();
this.setVisible(true);
}
public void paint(Graphics grp){
super.paint(grp);
imgPlane.paintIcon(this, grp, planeX, planeY);
imgBullet.paintIcon(this, grp, bulletX, bulletY);
}
public void run(){
while((bulletX > 0) &&(planeX < 400)){
repaint();
planeX = planeX + planeSpeed;
bulletX = bulletX - bulletSpeed;
try{
Thread.sleep(200);
}catch(Exception e){}
}
thread = null;
}
public void actionPerformed(ActionEvent aEvt){
JButton ob=(JButton)aEvt.getSource();
if(ob == btnUp){
planeY-=planeChangeSpeed;
}
if(ob == btnDown){
planeY += planeChangeSpeed;
}
}
public void keyPressed(KeyEvent e){
switch(e.getKeyCode()){
case KeyEvent.VK_UP:
planeY = planeY - 5;
break;
case KeyEvent.VK_DOWN:
planeY = planeY + 5;
break;
case KeyEvent.VK_LEFT:
planeX = planeX - 5;
break;
case KeyEvent.VK_RIGHT:
planeX = planeX + 5;
break;
}
}
public void keyTyped(KeyEvent e){}
public void keyReleased(KeyEvent e){}
public static void main(String args[]){
new Animation();
}
}

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

class Animation extends JFrame implements Runnable, ActionListener, KeyListener {
private Container cont;
private JButton btnUp;
private JButton btnDown;
private ImageIcon imgPlane;
private ImageIcon imgBullet;
private int planeX;
private int planeY;
private int bulletX;
private int bulletY;
private int planeSpeed;
private int bulletSpeed;
private int planeChangeSpeed;
private Thread thread;

private static Animation animation;//定义一个主界面的全局变量

public Animation() {
addKeyListener(this);
this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
GameStartInit();
}

public void GameStartInit() {
cont = this.getContentPane();
this.setBounds(0, 0, 400, 300);
cont.setLayout(null);
imgPlane = new ImageIcon("plane.gif");
imgBullet = new ImageIcon("bullet.gif");
planeX = 0;
planeY = 150;
bulletX = 400;
bulletY = 150;
planeSpeed = 8;
bulletSpeed = 8;
planeChangeSpeed = 6;
btnUp = new JButton("up");
btnDown = new JButton("down");
btnUp.setBounds(0, 240, 80, 30);
btnDown.setBounds(90, 240, 80, 30);
btnUp.addActionListener(this);
btnDown.addActionListener(this);
cont.add(btnUp);
cont.add(btnDown);
thread = new Thread(this);
thread.start();
this.setVisible(true);
this.requestFocus();//这里在定义完界面之后，再让主界面得到焦点，你原先键盘失灵的原因是，在运行的时候是按钮得到焦点，那么按键盘对按钮是没反应的
}

public void paint(Graphics grp) {
super.paint(grp);
imgPlane.paintIcon(this, grp, planeX, planeY);
imgBullet.paintIcon(this, grp, bulletX, bulletY);
}

public void run() {
while ((bulletX > 0) && (planeX < 400)) {
repaint();
planeX = planeX + planeSpeed;
bulletX = bulletX - bulletSpeed;
try {
Thread.sleep(200);
} catch (Exception e) {
}
}
thread = null;
}

public void actionPerformed(ActionEvent aEvt) {
JButton ob = (JButton) aEvt.getSource();
if (ob == btnUp) {
planeY -= planeChangeSpeed;
}
if (ob == btnDown) {
planeY += planeChangeSpeed;
}
animation.requestFocus();//每次按钮事件过后，都让主界面得到焦点，因为键盘事件是加载主界面上的
}

public void keyPressed(KeyEvent e) {
switch (e.getKeyCode()) {
case KeyEvent.VK_UP:
planeY = planeY - 5;
break;
case KeyEvent.VK_DOWN:
planeY = planeY + 5;
break;
case KeyEvent.VK_LEFT:
planeX = planeX - 5;
break;
case KeyEvent.VK_RIGHT:
planeX = planeX + 5;
break;
}
}

public void keyTyped(KeyEvent e) {
}

public void keyReleased(KeyEvent e) {
}

public static void main(String args[]) {
animation = new Animation();//定义了一个全局变量
}
}

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