键盘监听添加不上求解！！！！！！！

Question

新手想写个贪吃蛇的游戏，还有很多问题没有完善，现在遇到的问题是addkeylistener添加不上求解!import java.awt.*;
import java.awt.event.*;import javax.swing.*;public class SnakeGame extends JFrame{


private static final int STONE_HIGHT = 30;
//snakeZ表示蛇的前进方向1234分别代表东南西北
private int snakeZ=1,foodX,foodY,length=3;
private int m[]=new int[50];
private int n[]=new int[50];
private JPanel panel1,panel2;
private JButton butStart,butEsc,butStop,butResume;
private Canvas canvas=new Canvas()
{
public void paint( Graphics g )
{
drawStone(g);
drawSnake(g);
drawNet(g);
}
};

public SnakeGame()
{
setLayout(new BorderLayout());
setBounds(300, 100, 600, 600);
panel1=new JPanel();
//panel1.setBackground(Color.red);
panel2=new JPanel();
//panel2.setBackground(Color.green);
butStart=new JButton("开始游戏");
butEsc=new JButton("退出");
butStop=new JButton("暂停");
butResume=new JButton("继续");

add(panel1,BorderLayout.CENTER);
add(panel2,BorderLayout.SOUTH);
panel1.add(canvas);
canvas.setSize(600, 540);
canvas.setBackground(Color.gray);
panel2.setLayout(new GridLayout(1,4));
panel2.add(butEsc);
panel2.add(butResume);
panel2.add(butStart);
panel2.add(butStop);

m[0]=canvas.getWidth()/2;
n[0]=canvas.getHeight()/2;
for(int i=1;i<length;i++)
{
m[i]=m[i-1]+STONE_HIGHT;
n[i]=n[i-1];
}
//***************监听事件*************************
//开始键监听事件
butStart.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
thread t=new thread();
t.start();
}
});
//退出键监听事件
butEsc.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
System.exit(0);
}
});
//暂停键监听事件
butStop.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
System.out.println("暂停");
}
});
//继续键监听事件
butResume.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
System.out.println("继续");
}
});
addKeyListener(new KeyAdapter()
{
public void keyPressed(KeyEvent e) 
{
System.out.println("dfdsf");
switch(e.getKeyCode())
{
case KeyEvent.VK_UP:
if(snakeZ!=2) { snakeZ=4;System.out.println("dfdsfsd");refresh();}break;
case KeyEvent.VK_DOWN:
if(snakeZ!=4) {snakeZ=2;refresh();}break;
case KeyEvent.VK_LEFT:
if(snakeZ!=1) {snakeZ=3;refresh();}break;
case KeyEvent.VK_RIGHT:
if(snakeZ!=3) {snakeZ=1;refresh();}break;
}

}
});
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}

public class thread extends Thread
{
public void run()
{
while(true)
{
refresh();
try
{
Thread.sleep(500);
}
catch(InterruptedException e)
{

}
}
}
}


public void drawStone(Graphics g)
{
g.setColor(Color.DARK_GRAY);
g.fillRect(0, 0, STONE_HIGHT, canvas.getHeight());
g.fillRect(0, 0, canvas.getWidth(), STONE_HIGHT);
g.fillRect(0, canvas.getHeight()-STONE_HIGHT, canvas.getWidth(), STONE_HIGHT);
g.fillRect(canvas.getWidth()-STONE_HIGHT, 0, canvas.getWidth(), canvas.getHeight());

}

public void drawNet(Graphics g)
{
g.setColor(Color.white);
for(int i=0;i<canvas.getWidth()/STONE_HIGHT;i++)
g.drawLine(i*STONE_HIGHT, 0, i*STONE_HIGHT, canvas.getHeight());
for(int i=0;i<canvas.getHeight()/STONE_HIGHT;i++)
g.drawLine(0, i*STONE_HIGHT, canvas.getWidth(), i*STONE_HIGHT);
}

public void drawSnake(Graphics g)
{
g.setColor(Color.blue);
for(int i=0;i<length;i++)
    g.fillRect(m[i], n[i], STONE_HIGHT,STONE_HIGHT);
}

public void refresh()
{
switch(snakeZ)
{
case 1:

for(int i=length;i>=0;i--)
{
m[i+1]=m[i];
n[i+1]=n[i];
}
m[0]=m[0]+STONE_HIGHT;break;
case 2:
for(int i=length;i>=0;i--)
{
int tempX=m[i];
int tempY=n[i];
m[i+1]=tempX;
n[i+1]=tempY;
}
n[0]=n[0]-STONE_HIGHT;break;
case 3:
for(int i=length;i>=0;i--)
{
int tempX=m[i];
int tempY=n[i];
m[i+1]=tempX;
n[i+1]=tempY;
}
m[0]=m[0]-STONE_HIGHT;break;
case 4:
for(int i=0;i<length-1;i++)
{
int tempX=m[i];
int tempY=n[i];
m[i+1]=tempX;
n[i+1]=tempY;
}
n[0]=n[0]+STONE_HIGHT;break;
}
canvas.repaint();
} public static void main ( String args[] )
{
new SnakeGame();
}
}

Answer 1

 this.addKeyListener(new KeyAdapter()
        {
            public void keyPressed(KeyEvent e) 
            {
................
这样看下   没测试过

Answer 2

当然不可以，组件只有获得焦点之后才能监听到键盘事件，把键盘监听器放到canvas上，canvas.addKeyListener , 然后在canvas.repaint();后添加canvas.requestFocusInWindow();
你先试试看