本题主窗口中包括一个文本框和一个文本域，在上面的文本框中输入一个整数并按回车键，就会在下面的文本域中显示该整数的平方值；如果在文本框中输入的不是一个整数，将弹出一个警告窗口。
import java. awt. event. * ;
import java. awt. * ;
import javax. swing. JOptionPane;
class Dwindow extends Frame implements ActionListener
TextField inputNumber;
TextArea show;
Dwindow(String s)
super(s);
inputNumber=new TextField(22);
inputNumber. addActionListener(this);
show=new TextArea();
add(inputNumber, BorderLayout. NORT H);
add(show, BorderLayout. CENTER);
setBounds(60,60,300,300); setVisible(true);
validate();
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System. exit(0);

);

public void actionPerformed(ActionEvent e)
boolean boo=false;
if(e. getSource()==inputNumber)
String s=______;
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",
______);
inputNumber. setText(null);

else if(boo==false)
int number=Integer. parselnt(s);
show. append("\n"+number+"平方:"+(num-ber*number));




public class java2
public static void main(String args[])
new Dwindow("java2");