下面的程序哪里出错？为什么我移动W,A,S,D键的时候坦克的方向不改变呢？
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class Demo extends JFrame {

Mypanel mp = null;

public static void main(String[] args) {
Demo mtg = new Demo();

}
public Demo() {
mp = new Mypanel();

Thread t=new Thread(mp);
t.start();
this.add(mp);

this.addKeyListener(mp);
this.setSize(800,700);

this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);
}
}
class Mypanel extends JPanel implements KeyListener ,Runnable{

int x=100;
int y=100;

int direct=0;
int speed=1;
int color;
public void paint(Graphics g){
super.paint(g);

g.setColor(Color.yellow);
g.fill3DRect(x+11,y+12,50,5,false);
g.fill3DRect(x+11,y+44,50,5,false);
g.setColor(Color.red);
g.fillRect(x+19,y+15,30,30);
g.setColor(Color.BLUE);
g.fillOval(x+23, y+18, 23,23);
g.setColor(Color.black);
g.drawLine(x+34,y+30,x+71,y+30);

}
public void move(){
Graphics g = null;
switch(direct){
case 0:
g.setColor(Color.yellow);
g.fill3DRect(x+17,y+5,5,50,false);
g.fill3DRect(x+48,y+5,5,50,false);
g.setColor(Color.red);
g.fillRect(x+19,y+15,30,30);
g.setColor(Color.BLUE);
g.fillOval(x+23, y+18, 23,23);
g.setColor(Color.green);
g.drawLine(x+34,y+34,x+34,y-3);
break;
case 1:
g.setColor(Color.yellow);
g.fill3DRect(x+11,y+12,50,5,false);
g.fill3DRect(x+11,y+44,50,5,false);
g.setColor(Color.red);
g.fillRect(x+19,y+15,30,30);
g.setColor(Color.BLUE);
g.fillOval(x+23, y+18, 23,23);
g.setColor(Color.green);
g.drawLine(x+34,y+30,x-4,y+30);
break;

case 2:
g.setColor(Color.yellow);
g.fill3DRect(x+17,y+5,5,50,false);
g.fill3DRect(x+48,y+5,5,50,false);
g.setColor(Color.red);
g.fillRect(x+19,y+15,30,30);
g.setColor(Color.BLUE);
g.fillOval(x+23, y+18, 23,23);
g.setColor(Color.green);
g.drawLine(x+34,y+34,x+34,y+71);
break;
case 3:
g.setColor(Color.yellow);
g.fill3DRect(x+11,y+12,50,5,false);
g.fill3DRect(x+11,y+44,50,5,false);
g.setColor(Color.red);
g.fillRect(x+19,y+15,30,30);
g.setColor(Color.BLUE);
g.fillOval(x+23, y+18, 23,23);
g.setColor(Color.green);
g.drawLine(x+34,y+30,x+71,y+30);
break;
}

}


public void keyPressed(KeyEvent e) {


if (e.getKeyCode() == KeyEvent.VK_W)
{
this.setdirect(0);
y-=4;

} else if (e.getKeyCode() == KeyEvent.VK_D)
{
this.setdirect(1);
x+=4;


} else if (e.getKeyCode() == KeyEvent.VK_S)
{
this.setdirect(2);
y+=4;


} else if (e.getKeyCode() == KeyEvent.VK_A)
{
this.setdirect(3);
x-=4;

}
this.repaint();
}


private void setdirect(int i) {

}
public void keyReleased(KeyEvent arg0) {
}

public void keyTyped(KeyEvent arg0) {

}

public void run() {

}

}


[解决办法]
帮你改了一下，调试过可以了，你对比一下有什么不同吧：

Java code

import javax.swing.*;import java.awt.*;import java.awt.event.*;import java.util.*;public class Demo extends JFrame {  Mypanel mp = null;  public static void main(String[] args) {  Demo mtg = new Demo();  }  public Demo() {  mp = new Mypanel();    Thread t=new Thread(mp);  t.start();  this.add(mp);      this.addKeyListener(mp);  this.setSize(800,700);      this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  this.setVisible(true);  }}class Mypanel extends JPanel implements KeyListener ,Runnable{     int x=100;  int y=100;    int direct=0;  int speed=1;  int color;  public void paint(Graphics g){super.paint(g);/*g.setColor(Color.yellow);g.fill3DRect(x+11,y+12,50,5,false);g.fill3DRect(x+11,y+44,50,5,false);g.setColor(Color.red);g.fillRect(x+19,y+15,30,30);g.setColor(Color.BLUE);g.fillOval(x+23, y+18, 23,23);g.setColor(Color.black);g.drawLine(x+34,y+30,x+71,y+30);*/move(g);}  public void move(Graphics g){//Graphics g = null;switch(direct){case 0:g.setColor(Color.yellow);g.fill3DRect(x+17,y+5,5,50,false);g.fill3DRect(x+48,y+5,5,50,false);g.setColor(Color.red);g.fillRect(x+19,y+15,30,30);g.setColor(Color.BLUE);g.fillOval(x+23, y+18, 23,23);g.setColor(Color.green);g.drawLine(x+34,y+34,x+34,y-3);break;case 1:g.setColor(Color.yellow);g.fill3DRect(x+11,y+12,50,5,false);g.fill3DRect(x+11,y+44,50,5,false);g.setColor(Color.red);g.fillRect(x+19,y+15,30,30);g.setColor(Color.BLUE);g.fillOval(x+23, y+18, 23,23);g.setColor(Color.green);//g.drawLine(x+34,y+30,x-4,y+30);g.drawLine(x+34,y+30,x+71,y+30);break;  case 2:g.setColor(Color.yellow);g.fill3DRect(x+17,y+5,5,50,false);g.fill3DRect(x+48,y+5,5,50,false);g.setColor(Color.red);g.fillRect(x+19,y+15,30,30);g.setColor(Color.BLUE);g.fillOval(x+23, y+18, 23,23);g.setColor(Color.green);g.drawLine(x+34,y+34,x+34,y+71);break;case 3:g.setColor(Color.yellow);g.fill3DRect(x+11,y+12,50,5,false);g.fill3DRect(x+11,y+44,50,5,false);g.setColor(Color.red);g.fillRect(x+19,y+15,30,30);g.setColor(Color.BLUE);g.fillOval(x+23, y+18, 23,23);g.setColor(Color.green);//g.drawLine(x+34,y+30,x+71,y+30);g.drawLine(x+34,y+30,x-4,y+30);break;}    }      public void keyPressed(KeyEvent e) {          if (e.getKeyCode() == KeyEvent.VK_W)  {     this.setdirect(0);y-=4;      } else if (e.getKeyCode() == KeyEvent.VK_D)  {  this.setdirect(1);  x+=4;      } else if (e.getKeyCode() == KeyEvent.VK_S)  {  this.setdirect(2);y+=4;    } else if (e.getKeyCode() == KeyEvent.VK_A)    {  this.setdirect(3);x-=4;  }  this.repaint();    }private void setdirect(int i) {    this.direct=i;}public void keyReleased(KeyEvent arg0) {  }  public void keyTyped(KeyEvent arg0) {  }public void run() {}}