老是空指针异常，改了好些遍，都没成功，大家帮我看一下吧

在你注释的地方你是声明了一个 myPanel变量，但是你没有给这个变量赋一个对象，这个变量的引用就是null，所以会报exception。你可以把 myPanel打印出来看看是不是null

[此贴子已经被作者于2016-7-15 18:23编辑过]

package demo01;

import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test01 extends JFrame {
    MyJPanel myPanel;
   
    public static void main(String[] args) {
        Test01 demo = new Test01();
    }
   
    public Test01(){
        myPanel = new MyJPanel();
        //System.out.println(myPanel);
        this.add(myPanel);
        MyListener listener = new MyListener(this.myPanel);
        this.addKeyListener(listener);
        this.setSize(400,300);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);
        this.setVisible(true);
    }
}

class MyJPanel extends JPanel{
    int x = 10;
    int y = 10;
    int speed = 1;
   
    public int getSpeed() {
        return speed;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }

    public int getX() {
        return x;
    }
   
    public void setX(int x) {
        this.x = x;
    }
   
    public int getY() {
        return y;
    }
   
    public void setY(int y) {
        this.y = y;
    }
   
   
    public void paint(Graphics g){
        super.paint(g);
        g.fillOval(x,y,10,10);
    }
}

class MyListener implements KeyListener{
   
    MyJPanel myPanel ;
   
        //此处报告空指针异常
   /* int x = myPanel.getX();
    int y = myPanel.getY();*/
    int x;
    int y;
    int speed;
    //int speed = myPanel.getSpeed();
   
    public MyListener(){
        
    }
   //修改之后
    public MyListener(MyJPanel myPanel){
        this.myPanel = myPanel;
        x = myPanel.getX();
        y = myPanel.getY();
        speed = myPanel.getSpeed();
    }
   
    public void keyTyped(KeyEvent e) {
        
    }

   
    public void keyPressed(KeyEvent e) {
        
        if (e.getKeyCode() == KeyEvent.VK_W) {
            myPanel.setY(y - speed -10);
        } else if (e.getKeyCode() == KeyEvent.VK_S) {
            myPanel.setY(y + speed  +10);
        } else if (e.getKeyCode() == KeyEvent.VK_A) {
            myPanel.setX(x - speed-10);
        } else if (e.getKeyCode() == KeyEvent.VK_D) {
            myPanel.setX(x + speed +10);
        }
        myPanel.repaint();
        
    }

   
    public void keyReleased(KeyEvent e) {
        
    }
   
}

这样修改可以运行