// The Calculator example using the swing package

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class Calculator extends JPanel implements ActionListener {

   float number1, number2, result;
   JLabel label1, label2, label3, title;
   JTextField input1, input2, input3;
   String operation;

   // Constructor for the Calculator class

   public Calculator () {

     setLayout (new FlowLayout());

     title = new JLabel ("Calculator program");

     label1 = new JLabel ("Enter the first number: ");
     label2 = new JLabel ("Enter the second number: ");
     label3 = new JLabel ("Enter the operation (+, -, *, or /): ");

     input1 = new JTextField (8);
     input2 = new JTextField (8);
     input3 = new JTextField (1);

     add (title);
     add (label1);
     add (input1);
     add (label2);
     add (input2);
     add (label3);
     add (input3);    
     input3.addActionListener(this);

     number1 = 0;
     number2 = 0;
     operation = "";

     setPreferredSize (new Dimension(200,400));

   }

   public void paintComponent (Graphics g) {

    super.paintComponent (g); // must be present for the repaint method to work properly

    if (operation.equals (""));
    else if ((operation.equals ("/")) & (number2 == 0))
       g.drawString ("Division by zero is not permitted", 10, 250);
       else
          g.drawString (number1 + " " + operation + " " + number2 + " = " + result, 30, 250);

   }   

   public void actionPerformed (ActionEvent e) {

     number1 = Float.parseFloat(input1.getText());
     number2 = Float.parseFloat(input2.getText());
     operation = input3.getText();

     if (operation.equals ("+"))
        result = number1 + number2;
     else if (operation.equals ("-"))
        result = number1 - number2;
     else if (operation.equals ("*"))
        result = number1 * number2;
     else {
        if (number2 == 0);
        else
           result = number1 / number2;
     }
        
     repaint();
   }

}

class CalculatorGUI2 {


   public static void main (String[] args) {

   JFrame mywindow = new JFrame ("Calculator example");
   mywindow.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);


   mywindow.getContentPane().add (new Calculator ());


   mywindow.pack();
   mywindow.setVisible(true);   

   }
}