编写Applet程序实现一个计算器，包括10个数字（0~9）按钮和4个运算符（加、减、乘、除）按钮，以及等号和清空两个辅助按钮，还有一个显示输入输出的文本框。试用GridLayout实现之

import java.awt.*;
import java.awt.event.*;
public class Calculator extends Frame implements ActionListener{
private double a=0, b=0, sum=0;
int flag=0, count=0,p=1;
char mode='?';	//本次运算的符号
private TextField display = new TextField();
private Button one = new Button("1");
private Button two = new Button("2");
private Button three = new Button("3");
private Button four = new Button("4");
private Button five = new Button("5");
private Button six = new Button("6");
private Button seven = new Button("7");
private Button eight = new Button("8");
private Button nine = new Button("9");
private Button zero = new Button("0");
private Button point = new Button(".");
private Button add = new Button("+");
private Button sub = new Button("-");
private Button mul = new Button("×");
private Button div = new Button("÷");
private Button result = new Button("=");
private Button clr = new Button("CLR");
private Button quit = new Button("quit");
private Label label = new Label("calculator");

private class WindowCloser extends WindowAdapter{
public void windowClosing(WindowEvent we)
{	System.exit(0);	}
}
//布局
private void setup() {
Panel top = new Panel();
top.setLayout(new GridLayout(2,1));
top.add(label);
top.add(display);
Panel number = new Panel();
number.setLayout(new GridLayout(6,3));
number.add(one); number.add(four); number.add(seven);
number.add(two); number.add(five); number.add(eight);
number.add(three); number.add(six); number.add(nine);
number.add(zero); number.add(add); number.add(sub);
number.add(point); number.add(mul); number.add(div);
number.add(result); number.add(clr); number.add(quit);
setLayout(new BorderLayout()); add("North",top);
add("South",number);
}

//构造方法
public Calculator() {
super("Calculator");
setup();
one.addActionListener(this);
two.addActionListener(this);
three.addActionListener(this);
four.addActionListener(this);
five.addActionListener(this);
six.addActionListener(this);
seven.addActionListener(this);
eight.addActionListener(this);
nine.addActionListener(this);
zero.addActionListener(this);
point.addActionListener(this);
add.addActionListener(this);
sub.addActionListener(this);
mul.addActionListener(this);
div.addActionListener(this);
clr.addActionListener(this);
quit.addActionListener(this);
result.addActionListener(this);
addWindowListener(new WindowCloser());
pack();	setSize(200,222);
setVisible(true);
}
void reset0() {
a=0; b=0; count=0; sum=0; p=1; mode='?';
}
void setAndDis(char c) {
count=0; flag=0;
a=Double.parseDouble(display.getText());
mode=c;
}
//说明单击按钮以后要采取的行动
public void actionPerformed(ActionEvent ae) {
if(ae.getSource() == quit)
System.exit(0);
if(ae.getSource() == clr) {
reset0();
flag=0;
display.setText("0");
}else if(ae.getSource() == zero) {
if(count != 0) {
reset0();
}
if(flag == 0) {
display.setText("0");
flag=1;
}else display.setText(display.getText()+"0");
}
//输入0~9
if(ae.getSource() == one) {
if(count != 0) {
reset0();
}if(flag == 0||display.getText().equals("0")) {
display.setText("1");
flag=1;
}else display.setText(display.getText()+"1");
}

if(ae.getSource() == two)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("2");
flag=1;
}else display.setText(display.getText()+"2");
}

if(ae.getSource() == three)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("3");
flag=1;
}else display.setText(display.getText()+"3");
}

if(ae.getSource() == four)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("4");
flag=1;
}else display.setText(display.getText()+"4");
}

if(ae.getSource() == five)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("5");
flag=1;
}else display.setText(display.getText()+"5");
}

if(ae.getSource() == six)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("6");
flag=1;
}else display.setText(display.getText()+"6");
}

if(ae.getSource() == seven)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("7");
flag=1;
}else display.setText(display.getText()+"7");
}

if(ae.getSource() == eight)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("8");
flag=1;
}else display.setText(display.getText()+"8");
}

if(ae.getSource() == nine)
{
if(count != 0) {
reset0();
}
if(flag == 0||display.getText().equals("0")) {
display.setText("9");
flag=1;
}else display.setText(display.getText()+"9");
}

if(ae.getSource() == point) {
if(flag == 1 && p != 0) {
display.setText(display.getText()+".");
p=0;
}
}
//输入+，-，×，÷
if(ae.getSource() == add) {
setAndDis('+');
}
if(ae.getSource() == sub) {
setAndDis('-');
}
if(ae.getSource() == mul) {
setAndDis('×');
}
if(ae.getSource() == div) {
setAndDis('÷');
}

if((ae.getSource() == result)&&mode != '?') {
flag=0;
if(count == 0) {
b=Double.parseDouble(display.getText());
count=1;
}
sum=run(a,b,mode);
a=sum;
display.setText(String.valueOf(sum));
}
}
public double run(double a, double b, char mode) {
double sum=0;
if(mode == '+') sum=a+b;
if(mode == '-') sum=a-b;
if(mode == '×') sum=a*b;
if(mode == '÷') sum=a/b;
return(sum);
}
public static void main(String[] args) {
Calculator cal = new Calculator();
}
}