请问这段程序怎么就是呢？

来源：百度知道 编辑：UC知道 时间：2024/06/29 22:24:23
看得挺多，其实连布局管理器都没用上，就是定义一些gui组件加到面板上，把面板再加到窗体上。编译通过，但是运行时显示如下错误：
Exception in thread "main" java.lang.NullPointerExcep
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at Registration.<init>(Registration.java:48)
at Registration.main(Registration.java:59)
这是怎么回事？我用jdk字符界面这样，用eclipse，netbeans都是显示这些。
import java.awt.*;
public class Registration{
Frame frame;
Panel panel;
Label lblUser,lblPwd,lblConfirm,lblBlood,lblIntro,lblWay;
TextField textUser,textPwd,textConfirm;
TextArea areaIntro;
Choice choBlood;
List listWay;
Checkbox checkAccept;
Button buttonOk,buttonCancel;
public Registration(){
frame=new Frame("用户注册--AWT常用组件演示程序");
panel=new Panel();
frame.add(panel);
lblUser=new Label("注册名");
lblPwd=new Label("密码&qu

import java.awt.*;
public class Registration extends Frame{
Frame frame;
Panel panel;
Label lblUser,lblPwd,lblConfirm,lblBlood,lblIntro,lblWay;
TextField textUser,textPwd,textConfirm;
TextArea areaIntro;
Choice choBlood;
List listWay;
Checkbox checkAccept;
Button buttonOk,buttonCancel;
public Registration(){
super("用户注册--AWT常用组件演示程序");
setSize(420,210);
setVisible(true);

lblUser=new Label("注册名");
lblPwd=new Label("密码");
lblConfirm=new Label("确认密码");
lblBlood=new Label("血型");
lblWay=new Label("了解本网站的途径");
textUser=new TextField(15);
textPwd=new TextField(15);
textConfirm=new TextField(15);
textPwd.setEchoChar('*');
textConfirm.setEchoChar('*');
choBlood=new Choice();
choBlood.addItem("A型");
choBlood.addItem("B型");
choBl