import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class WebCalculator extends Applet 
    implements ActionListener, TextListener
{
  private TextField inputOne, inputTwo, output;
  private Panel opsPad;
  private Checkbox addBox, subtractBox;
  private CheckboxGroup ops;
  private Button equals;

  private Calculator calc;

  private void add()
  {
    double result;

    result = calc.add();

    output.setText (Double.toString(result));
  }

  private void subtract()
  {
    double result;

    result = calc.subtract ();

    output.setText (Double.toString(result));
  }

  public void init()
  {
    inputOne = new TextField ("0");
    inputTwo = new TextField ("0");
    output = new TextField ("0");
    
    opsPad = new Panel();
    opsPad.setLayout(new GridLayout(2,1));

    CheckboxGroup ops = new CheckboxGroup();
   
    addBox = new Checkbox ("+", ops, true);
    subtractBox = new Checkbox ("-", ops, false);

    opsPad.add (addBox);
    opsPad.add (subtractBox);

    equals = new Button ("=");

    setLayout(new GridLayout(1,5));
    add (inputOne);
    add (opsPad);
    add (inputTwo);
    add (equals);
    add (output);

    calc = new Calculator();

    equals.addActionListener (this);
    inputOne.addTextListener (this);
    inputTwo.addTextListener (this);
  }

  public void actionPerformed (ActionEvent evt)
  {
    if (addBox.getState())
      add();
    else
      subtract();
  }

  public void textValueChanged (TextEvent evt)
  {
    Double d; 
    if (evt.getSource() == inputOne)
    {
      d = new Double (inputOne.getText());
      calc.setLeftOperand(d.doubleValue());
    }

    if (evt.getSource() == inputTwo)
    {
      d = new Double (inputTwo.getText());
      calc.setRightOperand(d.doubleValue());
    }
  }
}