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

/**
 GUI for totaling a series of numbers.
*/
public class Adder extends JFrame implements ActionListener
{
    public static final int WIDTH = 400;
    public static final int HEIGHT = 200;

    private JTextField inputOutputField;
    private double sum = 0;

    public static void main(String[] args)
    {
        Adder guiAdder = new Adder( );
        guiAdder.setVisible(true);
    }

    public Adder( )
    {
        setTitle("Adding Machine");
        addWindowListener(new WindowDestroyer( ));
        setSize(WIDTH, HEIGHT);
        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( ));
    }
}