Java/Swing Components/Calculator

Popup Calculator

   <source lang="java">

/**

* @version 1.20 27 Jun 1998
* @author Cay Horstmann
*/

import java.awt.BorderLayout; import java.awt.Button; import java.awt.Container; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JApplet; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JTextField; public class PopupCalculatorApplet extends JApplet implements ActionListener {

 public void init() {
   Button calcButton = new Button("Calculator");
   calcButton.addActionListener(this);
   Container contentPane = getContentPane();
   contentPane.add(calcButton);
 }
 public void actionPerformed(ActionEvent evt) {
   if (calc.isVisible())
     calc.setVisible(false);
   else
     calc.show();
 }
 private JFrame calc = new CalculatorFrame();

} class CalculatorPanel extends JPanel implements ActionListener {

 public CalculatorPanel() {
   setLayout(new BorderLayout());
   display = new JTextField("0");
   display.setEditable(false);
   add(display, "North");
   JPanel p = new JPanel();
   p.setLayout(new GridLayout(4, 4));
   String buttons = "789/456*123-0.=+";
   for (int i = 0; i < buttons.length(); i++)
     addButton(p, buttons.substring(i, i + 1));
   add(p, "Center");
 }
 private void addButton(Container c, String s) {
   JButton b = new JButton(s);
   c.add(b);
   b.addActionListener(this);
 }
 public void actionPerformed(ActionEvent evt) {
   String s = evt.getActionCommand();
   if ("0" <= s.charAt(0) && s.charAt(0) <= "9" || s.equals(".")) {
     if (start)
       display.setText(s);
     else
       display.setText(display.getText() + s);
     start = false;
   } else {
     if (start) {
       if (s.equals("-")) {
         display.setText(s);
         start = false;
       } else
         op = s;
     } else {
       calculate(Double.parseDouble(display.getText()));
       op = s;
       start = true;
     }
   }
 }
 public void calculate(double n) {
   if (op.equals("+"))
     arg += n;
   else if (op.equals("-"))
     arg -= n;
   else if (op.equals("*"))
     arg *= n;
   else if (op.equals("/"))
     arg /= n;
   else if (op.equals("="))
     arg = n;
   display.setText("" + arg);
 }
 private JTextField display;
 private double arg = 0;
 private String op = "=";
 private boolean start = true;

} class CalculatorFrame extends JFrame {

 public CalculatorFrame() {
   setTitle("Calculator");
   setSize(200, 200);
   Container contentPane = getContentPane();
   contentPane.add(new CalculatorPanel());
 }

}

      </source>