import java.awt.*;import java.awt.event.*;
import javax.swing.JOptionPane;
public class Example16_3
{
 public static void main(String args[])
 {
  new DWindow("带消息框的窗口");
 }
};
class DWindow extends Frame implements ActionListener
{
 TextField inputNumber;
 TextArea text;
 DWindow(String s)
 {
  super(s);
  //setLayout(new FlowLayout());
  setResizable(false);
  
  inputNumber=new TextField(20);
  text=new TextArea(10,20);
  inputNumber.addActionListener(this);
  add(inputNumber,BorderLayout.NORTH);
  add(text,BorderLayout.CENTER);
  setBounds(0,0,200,300);//validate();
  setVisible(true);
  addWindowListener(new WindowAdapter()
   {
    public void WindowClosing(WindowEvent e)
    {
     System.exit(0);
    }
   });
  validate();
 }
 public void actionPerformed(ActionEvent e)
 {
  boolean boo=false;
  if (e.getSource()==inputNumber)
  {
   String s=new String(inputNumber.getText());
   char a[]=s.toCharArray();
   for (int i=0;i<a.length;i++)
   {
    if (!(Character.isDigit(a[i])))
    {
     boo=true;
    }
   }
   if (boo==true)
   {
    JOptionPane.showMessageDialog(this,"您输入了非法字符。","警告对话框",JOptionPane.WARNING_MESSAGE);
    inputNumber.setText(null);
   }
   else if(boo=false)
   {
    int number=Integer.parseInt(s);
    text.append("\n"+number+"平方："+(number*number));
   }
  }
 }
};