编写APPLET程序，从键盘输入一个整数，判断是否为回文并在屏幕上输出

import java.applet.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class test extends Applet implements ActionListener

{
Label lb1,lb2;
TextField tf;
Button btn;
public void init()
{
lb1 = new Label("请输入一个整数:");
lb2 = new Label(" ");
tf = new TextField(10);
btn = new Button("判断");
setLayout(new FlowLayout());
add(lb1);
add(tf);
add(btn);
add(lb2);
btn.addActionListener(this);
setSize(200,200);
setVisible(true);
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==btn)
{
StringBuffer source = new StringBuffer(tf.getText());
source.reverse();
String reverseString = new String(source);
if(reverseString.equals(tf.getText()))