求一个Java Applet计算器源代码

这个也是我从别人那拿的 大家彼此交流交流哈
CalculatorPanel.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class CalculatorPanel extends JPanel{
public CalculatorPanel(){
setLayout(new BorderLayout());
result=0;
lastCommand="=";
start=true;
display=new JButton("0");
display.setEnabled(false);
add(display,BorderLayout.NORTH);

ActionListener insert =new InsertAction();
ActionListener command =new CommandAction();
panel=new JPanel();
panel.setLayout(new GridLayout(4,4));
addButton("7",insert);
addButton("8",insert);
addButton("9",insert);
addButton("/",command);

addButton("4",insert);
addButton("5",insert);
addButton("6",insert);
addButton("*",command);

addButton("1",insert);
addButton("2"