出现一个莫名其妙的异常，哪位好心人帮忙看看程序，感激不尽！！

求热心人帮忙解答，小弟快郁闷死了！！！感激不尽！！！
小弟写了一个applet，是想实现对一幅图进行猜价游戏，界面很简单，图片我也是放在确定正确的地方了，但是getCodeBase（）老是出现异常，小弟加了一些出错判断的语句，具体异常和代码如下：
代码：
import java.awt.*;

import java.applet.*;

import java.net.*;

import java.awt.event.*;

public class Lucky extends Applet implements ActionListener {

    Panel pNorth = new Panel();

    PicPanel pCenter = new PicPanel();

    Panel pBottom = new Panel();

    TextField txfield = new TextField(10);

    Label label = new Label("请开始游戏,按确定开始：");

    private int nPrice = 1100;

    private Image m_img;

    private boolean t = false;

    public Lucky() {

        super();

        this.setLayout(new BorderLayout());

        pNorth.add(label);

        pNorth.add(txfield);

        add(pNorth, BorderLayout.NORTH);

        add(pCenter, BorderLayout.CENTER);

        Button btnStart = new Button("开始游戏");

        Button btnOK = new Button("确定");

        Button btnCancel = new Button("取消");

        btnOK.setActionCommand("ok");

        btnStart.setActionCommand("start");

        btnCancel.setActionCommand("cancel");

        btnOK.addActionListener(this);

        btnStart.addActionListener(this);

        btnCancel.addActionListener(this);

        pBottom.add(btnStart);

        pBottom.add(btnOK);

        pBottom.add(btnCancel);

        add(pBottom, BorderLayout.SOUTH);

        setBackground(Color.white);

        String filename = "Image.gif";

        try {

            System.out.println(getCodeBase());

            m_img = getImage(getCodeBase(), "Image.gif");

        } catch (Exception e) {

            System.out.println("No Picture!");

            e.printStackTrace();

        }

        MediaTracker mt = new MediaTracker(this);

        mt.addImage(m_img, 0);

        try {

            mt.waitForID(0);

            t = mt.checkAll();

        } catch (Exception e) {

            e.printStackTrace();

            System.out.println();

            System.out.println(t);

            System.out.println("Loading Error!");

        }

        repaint();

    }

    public void init() {

    }

    public void paint(Graphics g) {

        System.out.println("Begin Drawing!");

        g.drawImage(m_img, 125, 0, 50, 160, this);

    }

    public void actionPerformed(ActionEvent evt) {

        if (evt.getActionCommand().equals("start")) {

            pCenter.initImg();

            label.setText("请输入商品估价");

            pCenter.repaint();

        } else if (evt.getActionCommand().equals("ok")) {

            int guessprice = 0;

            try {

                guessprice = Integer.parseInt(txfield.getText().trim());

                String guess = comparePrice(guessprice);

                new MsgDlg(guess);

            } catch (Exception e) {

                e.printStackTrace();

            }

        } else if (evt.getActionCommand().equals("cancel")) {

            txfield.setText("");

        }

    }

    public String comparePrice(int guessPrice) {

        if (guessPrice == nPrice) {

            return "答对了";

        } else if (guessPrice > nPrice) {

            return "估价过高！";

        } else {

            return "估价过低！";

        }

    }

}

class PicPanel extends Panel {

    private Image m_img;

    public void initImg() {

    }

}

class MsgDlg extends Frame implements ActionListener {

    Label label = new Label();

    public MsgDlg(String strMsg) {

        super();

        setTitle("猜的结果");

        Panel p = new Panel();

        add(p);

        p.add(label);

        label.setText(strMsg);

        setSize(150, 100);

        setLocation(300, 200);

        Button btnOK = new Button("确定");

        btnOK.addActionListener(this);

        p.add(btnOK);

        show();

    }

    public void actionPerformed(ActionEvent evt) {

        this.dispose();

    }

}

异常如下：
java.lang.NullPointerException
  at java.applet.Applet.getCodeBase(Applet.java:136)
  at lucky.Lucky.<init>(Lucky.java:55)
  at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
  at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
  at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
  at java.lang.reflect.Constructor.newInstance(Constructor.java:274)
  at java.lang.Class.newInstance0(Class.java:308)
No Picture!//这句是自己加的出错提示

  at java.lang.Class.newInstance(Class.java:261)
  at com.borland.jbuilder.runtime.applet.AppletTestbed.a(Unknown Source)
  at com.borland.jbuilder.runtime.applet.AppletTestbed.startApplet(Unknown Source)
  at com.borland.jbuilder.runtime.applet.AppletTestbed.main(Unknown Source)
java.lang.NullPointerException
  at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2718)
  at sun.java2d.SunGraphics2D.drawImage(SunGraphics2D.java:2679)
  at lucky.Lucky.paint(Lucky.java:83)
  at sun.awt.RepaintArea.paint(RepaintArea.java:177)
  at sun.awt.windows.WComponentPeer.handleEvent(WComponentPeer.java:260)
  at java.awt.Component.dispatchEventImpl(Component.java:3678)
  at java.awt.Container.dispatchEventImpl(Container.java:1627)
  at java.awt.Component.dispatchEvent(Component.java:3477)
  at java.awt.EventQueue.dispatchEvent(EventQueue.java:456)
  at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
  at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
  at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
  at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)
Begin Drawing!//这句也是自己加的判断

8 个解决方案

#1

将构造方法中的代码移到init()方法中(super()除外)

#2

你写的代码好乱啊,用什么工具写的啊
因多写一点的注释!!!!记得喔

#3

Applet的生命周期是从 inti() 方法初始化开始然后再自动调用start() 方法，
所以你应该把你的构造方法放在 inti() 里面覆盖它

#4

NullPointerException初始化的问题了

#5

空指针异常，你的55，83行看看

#6

可能文件名大小写的问题image.gif

#7

谢谢yaray和learlee，问题已经解决，分也给了，再次谢谢

#8

但是我想问问为什么把代码放在构造函数中就会出错呢？
Applet启动的顺序不是：构造函数－》init()－》paint()－》start（）么？
放在构造函数中为什么就会有Nopoint的异常？

#1