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

public class AdderApplet extends JApplet implements ActionListener
{
    private JTextField inputOutputField;
    private double sum = 0;

    public void init()
    {
        Container contentPane = getContentPane();
        contentPane.setLayout(new BorderLayout());

        JPanel buttonPanel = new JPanel();
        buttonPanel.setBackground(Color.gray);
        buttonPanel.setLayout(new FlowLayout());
        JButton addButton = new JButton("Add");
        addButton.addActionListener(this);
        buttonPanel.add(addButton);
        JButton resetButton = new JButton("Reset");
        resetButton.addActionListener(this);
        buttonPanel.add(resetButton);
        contentPane.add(buttonPanel, BorderLayout.SOUTH);

        JPanel textPanel = new JPanel();
        textPanel.setBackground(Color.blue);
        textPanel.setLayout(new FlowLayout());
        inputOutputField = new JTextField("Numbers go here.", 30);
        inputOutputField.setBackground(Color.white);
        textPanel.add(inputOutputField);
        contentPane.add(textPanel, BorderLayout.CENTER);
    }

    public void actionPerformed(ActionEvent e)
    {
        if (e.getActionCommand().equals("Add"))
        {
            sum = sum +
                stringToDouble(inputOutputField.getText());
            inputOutputField.setText(Double.toString(sum));
        }
        else if (e.getActionCommand().equals("Reset"))
        {
            sum = 0;
            inputOutputField.setText("0.0");
        }
        else
            inputOutputField.setText("Error in adder code.");
    }

    private static double stringToDouble(String stringObject)
    {
        return Double.parseDouble(stringObject.trim());
    }
}