运行时出现异常

import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Calculator
{public static void main(String[] args)
{CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}

class CalculatorFrame extends JFrame
{public static final int WIDTH=300;
public static final int HEIGHT=300;
public CalculatorFrame()
{setTitle("学生成绩管理系统");
setSize(WIDTH,HEIGHT);
Container contentPane=getContentPane();
CalculatorPanel panel=new CalculatorPanel();
contentPane.add(panel);
}
}

class CalculatorPanel extends JPanel
{private JTextField text1;
private JTextField text2;
private JTextField text3;
private JTextField text4;
private JTextField text5;
private JTextField text6;
private JButton button1;
private JButton button2;
private JButton button3;
private JButton button4;
private JLabel label1;
private JLabel label2;
private JLabel label3;
private JLabel label4;
private JLabel label5;
private JLabel label6;
private JPanel panel;
public CalculatorPanel()
{setLayout(new BorderLayout());
text1=new JTextField();
text2=new JTextField();
text3=new JTextField();
text4=new JTextField();
text5=new JTextField();
text6=new JTextField();
button1=new JButton("存储");
button1=new JButton("删除");
button1=new JButton("查询");
button1=new JButton("排序");
label1=new JLabel("学号：");
label2=new JLabel("年龄：");
label3=new JLabel("名字：");
label4=new JLabel("数学成绩：");
label5=new JLabel("英语成绩：");
label6=new JLabel("数据结构成绩：");
JPanel panel=new JPanel(new GridLayout(8,6));
panel.add(label1);
panel.add(text1);
panel.add(label2);
panel.add(text2);
panel.add(label3);
panel.add(text3);
panel.add(label4);
panel.add(text4);
panel.add(label5);
panel.add(text5);
panel.add(label6);
panel.add(text6);
panel.add(button1);
panel.add(button2);
panel.add(button3);
panel.add(button4);
add(panel,BorderLayout.CENTER);
}

}


错误如下
---------- java ----------
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1019)
at java.awt.Container.add(Container.java:351)
at CalculatorPanel.<init>(Calculator.java:76)
at CalculatorFrame.<init>(Calculator.java:21)
at Calculator.main(Calculator.java:8)

输出完成 (耗时: 1 秒) - 正常终止

那位帮帮忙
谢谢了

----------------解决方案--------------------------------------------------------

空指针异常
这么容易解决的异常
它已经提示你哪一行出错了
去找不就得了吗?

----------------解决方案--------------------------------------------------------

/*
* Calculator.java
*
* Created on 2006年11月14日, 下午9:03
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/

/**
*
* @author lbf
*/
import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Calculator
{public static void main(String[] args)
{CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}

class CalculatorFrame extends JFrame
{public static final int WIDTH=300;
public static final int HEIGHT=300;
public CalculatorFrame()
{setTitle("学生成绩管理系统");
setSize(WIDTH,HEIGHT);
Container contentPane=getContentPane();
CalculatorPanel panel=new CalculatorPanel();
contentPane.add(panel);
}
}

class CalculatorPanel extends JPanel
{private JTextField text1;
private JTextField text2;
private JTextField text3;
private JTextField text4;
private JTextField text5;
private JTextField text6;
private JButton button1;
private JButton button2;
private JButton button3;
private JButton button4;
private JLabel label1;
private JLabel label2;
private JLabel label3;
private JLabel label4;
private JLabel label5;
private JLabel label6;
private JPanel panel;
public CalculatorPanel()
{setLayout(new BorderLayout());
text1=new JTextField();
text2=new JTextField();
text3=new JTextField();
text4=new JTextField();
text5=new JTextField();
text6=new JTextField();
button1=new JButton("存储");
button2=new JButton("删除");
button3=new JButton("查询");
button4=new JButton("排序");
label1=new JLabel("学号：");
label2=new JLabel("年龄：");
label3=new JLabel("名字：");
label4=new JLabel("数学成绩：");
label5=new JLabel("英语成绩：");
label6=new JLabel("数据结构成绩：");
JPanel panel=new JPanel(new GridLayout(8,6));
panel.add(label1);
panel.add(text1);
panel.add(label2);
panel.add(text2);
panel.add(label3);
panel.add(text3);
panel.add(label4);
panel.add(text4);
panel.add(label5);
panel.add(text5);
panel.add(label6);
panel.add(text6);
panel.add(button1);
panel.add(button2);
panel.add(button3);
panel.add(button4);
add(panel,BorderLayout.CENTER);
}

}

写程序不但要仔细,还要自己能排除错误

----------------解决方案--------------------------------------------------------

楼主是不是用复制，忘了该名字！呵呵！！

----------------解决方案--------------------------------------------------------

哈哈 肯定是的 我也经常这么干 嘿嘿
----------------解决方案--------------------------------------------------------