jdk编写的小程序

[miaocat]

代码如下：编译无错
import java.awt.*;
import java.awt.event.*;
import java.lang.*;
public class StudentInfo{
private Frame frobj;
private Checkbox checkobj;
private CheckboxGroup groupobj;
private Checkbox checkobj1,checkobj2;
private TextField tfobj;
private List listobj;
private Choice choiceobj;
private TextArea taobj;
private Button butobj1,butobj2;
private Label labobj1,labobj2,labobj3,labobj4,labobj5;
private Panel
panelobj1,panelobj2,panelobj3,panelobj4,panelobj5,panelobj6;
public static void main(String args[]){
StudentInfo stuobj=new StudentInfo();
stuobj.create();
}
public void create()
{
frobj=new Frame("Student information example");
checkobj=new Checkbox("是否注册");
labobj1=new Label("姓名：");
groupobj=new CheckboxGroup();
checkobj1=new Checkbox("男",groupobj,false);
checkobj2=new Checkbox("女",groupobj,false);
labobj3=new Label("年级：");
listobj=new List(4,false);
listobj.add("一年级");
listobj.add("二年级");
listobj.add("三年级");
listobj.add("四年级");
labobj4=new Label("系别：");
choiceobj=new Choice();
choiceobj.add("计算机");
choiceobj.add("数学");
choiceobj.add("物理");
choiceobj.add("外语");
labobj5=new Label("显示一个学生所有信息:");
taobj=new TextArea();
butobj1=new Button("显示");
butobj2=new Button("保存");
panelobj1=new Panel();
panelobj2=new Panel();
panelobj3=new Panel();
panelobj4=new Panel();
panelobj5=new Panel();
panelobj6=new Panel();
//
panelobj1.setLayout(new FlowLayout(FlowLayout.CENTER,20,20));
panelobj1.add(checkobj);
panelobj1.add(labobj1);
panelobj1.add(tfobj);
//
panelobj2.setLayout(new GridLayout(3,1));
panelobj2.add(labobj2);
panelobj2.add(checkobj1);
panelobj2.add(checkobj2);
panelobj3.setLayout(new BorderLayout());
panelobj3.add("North",labobj3);
panelobj3.add("Center",listobj);
//
panelobj4.setLayout(new BorderLayout());
panelobj4.add("North",labobj4);
panelobj4.add("Center",choiceobj);
panelobj5.setLayout(new BorderLayout());
panelobj5.add("North",labobj5);
panelobj5.add("Center",taobj);
panelobj6.setLayout(new FlowLayout(FlowLayout.CENTER,80,20));
panelobj6.add(butobj1);
panelobj6.add(butobj2);
//
GridBagLayout gridbag=new GridBagLayout();
GridBagConstraints c=new GridBagConstraints();
frobj.setLayout(gridbag);
c.gridwidth=GridBagConstraints.REMAINDER;
c.weightx=1.0;
gridbag.setConstraints(panelobj1,c);
frobj.add(panelobj1);
//
c.anchor=GridBagConstraints.NORTH;
c.gridwidth=1;
c.gridheight=4;
c.weightx=1.0;
gridbag.setConstraints(panelobj2,c);
gridbag.setConstraints(panelobj3,c);
frobj.add(panelobj2);
frobj.add(panelobj3);
c.gridwidth=GridBagConstraints.REMAINDER;
gridbag.setConstraints(panelobj4,c);
frobj.add(panelobj4);
//
c.gridwidth=GridBagConstraints.REMAINDER;
c.gridheight=4;
c.weightx=1.0;
gridbag.setConstraints(panelobj5,c);
frobj.add(panelobj5);
c.gridwidth=GridBagConstraints.RELATIVE;
gridbag.setConstraints(panelobj6,c);
frobj.add(panelobj6);
frobj.pack();
frobj.setVisible(true);
}
}

运行出现如下错误：

D:\jdk1.3.1_09\test>java StudentInfo
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at StudentInfo.create(StudentInfo.java:55)
at StudentInfo.main(StudentInfo.java:19)

请问是什么原因?

[ajoke]

在把控件放到container中时，有的为null

[miaocat]

可否讲清楚点
我是按照教程一模一样做的
还是不太明白

[ajoke]

private TextField tfobj;

panelobj1.add(tfobj);

没有初始化
是不是写错了为 taobj = new TextArea();？？？

汗.....