一道java练习题，帮帮忙！
import java.awt.*;
import java.awt.event.*;
class MyDialog extends Dialog implements ActionListener
{ Label La1,La2;int message=1;
  TextField text1,text2;static int a,b;
  MyDialog(Frame f,String s,boolean b)
  { super(f,s,b);

  La1=new Label("Width:"); text1=new TextField(4);
   
  text2=new TextField(4);
   
  La2=new Label("Height:");
   
  text1.addActionListener(this);
  text2.addActionListener(this);
  add(La1);
  add(text1);
  add(La2);
  add(text2);
  setBounds(30,30,60,200);
  setVisible(true);
  validate();
  addWindowListener(new WindowAdapter()
  { public void windowClosing(WindowEvent e)
  {setVisible(false);message=0;}
  });
  }
  public int getMessage()
  {return message;}
  public void actionPerformed(ActionEvent e)
  {
  a=Integer.parseInt(text1.getText());
  b=Integer.parseInt(text2.getText());
   
  }
}
class Win extends Frame implements ActionListener
{
  TextArea text;MyDialog dialog;Button b;
  Win(String s)
  { setTitle(s);
  text=new TextArea(22,22);
  b=new Button("设置");
  b.addActionListener(this);dialog=new MyDialog(this,"对话框",true);
  add(b);add(text);
  setVisible(true);
  setLayout(new FlowLayout());
  setBounds(20,20,360,360);
  validate();addWindowListener(new WindowAdapter(){public void windowClosing(WindowEvent e){System.exit(0);}}) ;
  }
  public void actionPerformed(ActionEvent e)
  {if(e.getSource()==b){dialog.setVisible(true);}
  if(dialog.getMessage()==0){dialog.setVisible(false);text.setSize(MyDialog.a,MyDialog.b);}
  }
  
}

public class Examplej
{
  public static void main(String args[])
  {

  new Win("对话窗口");}
}

------解决方案--------------------
问题是什么。。。。。崩溃中。。 我在报空指针异常