编写一个Applet图形界面程序，使用“方法的递归引用”求用户输入的任意整数的阶乘。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class FactorialTest extends JApplet implements ActionListener{
JTextArea outputarea;
JTextField field;
String num;
public void init()
{
outputarea=new JTextArea(10,10);
field=new JTextField(10);
field.addActionListener(this);
Container container=getContentPane();
container.setLayout(new FlowLayout());
container.add(field);
container.add(outputarea);
}
public long factorial(long number)
{
if(number<=1)
return 1;
else
return number*factorial(number-1);
}
public void actionPerformed(ActionEvent event)
{
int a=Integer.parseInt(field.getText());
long b=factorial(a);
num=a+"!="+b+"\n";
outputarea.append(num);
fiel