Java Program for Calculator using Applet

*/
import java.awt.*;
import java.awt.event.*;

public class calculator extends java.applet.Applet implements ActionListener {
TextField txtTotal = new TextField("");
    Button button[] = new Button[10];
Button divide = new Button("/");
Button mult = new Button("*");
Button plus = new Button ("+");
Button minus = new Button("-");
Button isequalto = new Button("=");
Button clear = new Button("CA");
double num ,numtemp ;
int counter;
String strnum = "",strnumtemp = "" ;
String op = "";

public void operation() {
counter ++;
if (counter == 1) {
 numtemp = num;
 strnum = "";
 num = 0;
}else{
 if (op == "+") numtemp += num;
 else if (op == "-") numtemp -= num;
 else if (op == "*") numtemp = numtemp * num;
 else if (op == "/") numtemp = numtemp / num;
 strnumtemp = Double.toString(numtemp);
 txtTotal.setText(strnumtemp);
 strnum = "";
 num = 0;
}
}

public void init() {
setLayout(null);

plus.setBackground(Color.blue);
plus.setForeground(Color.white);
     minus.setBackground(Color.blue);
minus.setForeground(Color.white);
     divide.setBackground(Color.blue);
divide.setForeground(Color.white);
isequalto.setBackground(Color.blue);
isequalto.setForeground(Color.white);
mult.setBackground(Color.blue);
mult.setForeground(Color.white);
clear.setBackground(Color.blue);
clear.setForeground(Color.red);

for(int i = 0;i <= 9; i ++) {
button[i] = new Button(String.valueOf(i));
button[i].setBackground(Color.orange);
button[i].setForeground(Color.blue);
}

button[1].setBounds(0,53,67,53);
button[2].setBounds(67,53,67,53);
button[3].setBounds(134,53,67,53);
button[4].setBounds(0,106,67,53);
button[5].setBounds(67,106,67,53);
button[6].setBounds(134,106,67,53);
button[7].setBounds(0,159,67,53);
button[8].setBounds(67,159,67,53);
button[9].setBounds(134,159,67,53);

for (int i = 1;i <= 9; i ++) {
add(button[i]);
}

txtTotal.setBounds(0,0,200,53);
add(txtTotal);
plus.setBounds(0,212,67,53);
add(plus);
button[0].setBounds(67,212,67,53);
add(button[0]);
minus.setBounds(134,212,67,53);
add(minus);
divide.setBounds(134,264,67,53);
add(divide);
isequalto.setBounds(67,264,67,53);
add(isequalto);
mult.setBounds(0,264,67,53);
add(mult);
add(clear);
}

public void start() {
for(int i = 0;i <= 9; i ++) {
button[i].addActionListener(this);
}
plus.addActionListener(this);
minus.addActionListener(this);
divide.addActionListener(this);
mult.addActionListener(this);
isequalto.addActionListener(this);
clear.addActionListener(this);
}

public void stop() {
for(int i = 0;i <= 9; i ++) {
button[i].addActionListener(null);
}
plus.addActionListener(null);
minus.addActionListener(null);
divide.addActionListener(null);
mult.addActionListener(null);
isequalto.addActionListener(null);
clear.addActionListener(null);
}

public void actionPerformed(ActionEvent e) {
for(int i = 0;i <= 9; i++) {
if (e.getSource() == button[i]) {
  play(getCodeBase(),i + ".au");
  strnum += Integer.toString(i);
  txtTotal.setText(strnum);
  num = Double.valueOf(strnum).doubleValue();
}
}

        if (e.getSource() == plus) {
operation();
op = "+";
}

if (e.getSource() == minus) {
operation();
op = "-";
}

if (e.getSource() == divide) {
operation();
op = "/";
}

if (e.getSource() == mult) {
operation();
op = "*";
}

if (e.getSource() == isequalto) {
if (op == "+") numtemp += num;
else if (op == "-") numtemp -= num;
else if (op == "*") numtemp = numtemp * num;
else if (op == "/") numtemp = numtemp / num;

strnumtemp = Double.toString(numtemp);
txtTotal.setText(strnumtemp);
strnumtemp = "";
numtemp = 0;
strnum = "";
num = 0;
counter = 0;
}

if (e.getSource() == clear) {
txtTotal.setText("0");
strnumtemp = "";
numtemp = 0;
strnum = "";
num = 0;
counter = 0;
}
}
}