一个比较诡异的JAVA问题

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class  Examplehuitu
{
public static void main(String[] args) 
{
huitu hh=new huitu();
}
}class huitu extends JFrame implements ItemListener,ActionListener
{
Container con;

JComboBox list,list1,list2,list3,list4;
JLabel label,label1,label2,label3,label4,label5,label6;
Box box1,box2,box3,box4,box5,box6;
String s1,s2,s3,s4,s5;
JPanel panel1,panel2;
JTextField text1,text2,text3,text4,text5;
JButton button1,enter,close;
JDialog dialog1;
Graphics g;
public huitu()
{
box1=Box.createHorizontalBox();
box2=Box.createHorizontalBox();
box3=Box.createVerticalBox();
box4=Box.createHorizontalBox();
box5=Box.createHorizontalBox();
box6=Box.createVerticalBox();

text1=new JTextField(3);
text2=new JTextField(5);
text3=new JTextField(5);
text4=new JTextField(5);
text5=new JTextField(5); button1=new JButton("输入数据");
enter=new JButton("确定");
close=new JButton("关闭"); panel1=new JPanel();
panel1.setSize(500,600);
panel1.validate();
panel1.setVisible(true);



s1=new String("画直线");
s2=new String("画圆");
s3=new String("区域填充");
s4=new String("平移变换");
s5=new String("裁剪");
label=new JLabel("请选择:");
label1=new JLabel("线形");
label2=new JLabel("线宽");
label3=new JLabel("颜色");
label4=new JLabel("起点坐标");
label5=new JLabel("终点坐标");
list=new JComboBox();
list1=new JComboBox();
list2=new JComboBox();
list3=new JComboBox();
list4=new JComboBox();
//list.setMaximumRowCount(3);
list.addItem("从以下选项中选择：");
list.addItem(s1);
list.addItem(s2);
list.addItem(s3);
list.addItem(s4);
list.addItem(s5); list1.addItem("虚线");
list1.addItem("实线");
list2.addItem("红色");
list2.addItem("黑色");
list2.addItem("蓝色");
list2.addItem("绿色");
list2.addItem("黄色");
list2.addItem("粉红");
list2.addItem("紫色");
list2.addItem("青色");
list2.addItem("深灰色");
list2.addItem("灰色");
list2.addItem("桔黄色");
box1.add(label);
box1.add(Box.createHorizontalStrut(10));
box1.add(list); box2.add(label1);
box2.add(Box.createHorizontalStrut(5));
box2.add(list1);
box2.add(Box.createHorizontalStrut(5));
box2.add(label2);
box2.add(Box.createHorizontalStrut(5));
box2.add(text1);
box2.add(Box.createHorizontalStrut(5));
box2.add(label3);
box2.add(Box.createHorizontalStrut(5));
box2.add(list2);
box2.add(Box.createHorizontalStrut(5));
box2.add(button1);
box2.setVisible(false);
box3.add(box1);
box3.add(Box.createVerticalStrut(5));
box3.add(box2); dialog1=new JDialog(this,"请输入相关数据",true);
dialog1.setBounds(100,100,200,200);


panel2=new JPanel();
panel2.setSize(200,200);
box4.add(label4);
box4.add(Box.createHorizontalStrut(5));
box4.add(text2);
box4.add(Box.createHorizontalStrut(5));
box4.add(text3);
box5.add(label5);
box5.add(Box.createHorizontalStrut(5));
box5.add(text4);
box5.add(Box.createHorizontalStrut(5));
box5.add(text5);
box6.add(box4);
box6.add(Box.createVerticalStrut(5));
box6.add(box5);
panel2.add(box6);
panel2.add(enter);
panel2.add(close);
dialog1.add(panel2);

con=getContentPane();
con.setLayout(new BorderLayout());
g=panel1.getGraphics();
setSize(700,800);
con.add(box3,BorderLayout.NORTH);
con.add(panel1,BorderLayout.CENTER);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
list.addItemListener(this);
button1.addActionListener(this);
validate();

}
public void init1()
{
}
public void itemStateChanged(ItemEvent e)
{
if (list.getSelectedIndex()==1)
{
//con.add(box3,BorderLayout.NORTH);
box2.setVisible(true);
//con.add(panel1,BorderLayout.CENTER);
g =panel1.getGraphics();
con.validate();
init1();
}
} public void actionPerformed(ActionEvent e)
{
if (e.getSource()==button1)
{
dialog1.setVisible(true);
} /*if (e.getSource()==enter)
{
dialog1.setVisible(false);
}*/
}
}