How to create owr own calculater - Computers & Internet

For all os ? you must use java language! this is the code:

//<applet code="calmayank"height=300 width=300></applet>
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class calmayank extends JApplet
implements ActionListener
{
JTextField t1;

JButton b1,b2,b3,b4,b5,b6,b7,b8,b9,b10,
b11,b12,b13,b14,b15,b16,b17,b18,b19,b20;

GridLayout gl;
JPanel p1,p2,p3;

public void init()
{
gl=new GridLayout(5,4);
p1=new JPanel();
p2=new JPanel();
p3=new JPanel();
p1.setLayout(gl);
t1=new JTextField(17);
b1=new JButton("1");
b2=new JButton("2");
b3=new JButton("3");
b4=new JButton("4");
b5=new JButton("5");
b6=new JButton("6");
b7=new JButton("7");
b8=new JButton("8");
b9=new JButton("9");
b10=new JButton("0");
b11=new JButton("+");
b12=new JButton("-");
b13=new JButton("*");
b14=new JButton("/");
b15=new JButton("@");
b16=new JButton("$");
b17=new JButton("%");
b18=new JButton(".");
b19=new JButton("?");
b20=new JButton("=");


p2.add(t1);

p1.add(b1);
p1.add(b2);
p1.add(b3);
p1.add(b4);
p1.add(b5);
p1.add(b6);
p1.add(b7);
p1.add(b8);
p1.add(b9);
p1.add(b10);
p1.add(b11);
p1.add(b12);
p1.add(b13);
p1.add(b14);
p1.add(b15);
p1.add(b16);
p1.add(b17);
p1.add(b18);
p1.add(b19);
p1.add(b20);
p3.add(p2);
p3.add(p1);
getContentPane().add(p3);

b1.addActionListener(this);
b2.addActionListener(this);
b3.addActionListener(this);
b4.addActionListener(this);
b5.addActionListener(this);
b6.addActionListener(this);
b7.addActionListener(this);
b8.addActionListener(this);
b9.addActionListener(this);
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==b1)
{
t1.setText("1");
}
else if(e.getSource()==b2)
{
t1.setText("2");
}
else if(e.getSource()==b3)
{
t1.setText("3");
}
else if(e.getSource()==b4)
{
t1.setText("4");
}
else if(e.getSource()==b5)
{
t1.setText("5");
}
else if(e.getSource()==b6)
{
t1.setText("6");
}
else if(e.getSource()==b7)
{
t1.setText("7");
}
else if(e.getSource()==b8)
{
t1.setText("8");
}
else if(e.getSource()==b9)
{
t1.setText("9");
}
}
}