import javax.swing.JFrame;
import javax.swing.JTextField;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JButton;
import java.awt.Color;


public class MyFrame extends JFrame implements ActionListener
{
    private JTextField operand1;
    private JTextField operand2;
    private JButton aButton;

    public MyFrame()
    {
	   initializeWidgets();
	   setSize (400,300);
	   addWidgets();
	   setLayout(null);
	   setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    }

    public void addWidgets()
    {
	   add(operand1);
	   add(operand2);
	   add(aButton);
    }

    // The is listener for button events but the button event
    // can change the state of the container (MyFrame) because
    // the container is the listener of button events.
    public void actionPerformed(ActionEvent anEvent)
    {
	   double number1 = Double.parseDouble(operand1.getText());
	   double number2 = Double.parseDouble(operand2.getText());
	   double sum = number1 + number2;
	   String resultExpression;
	   JButton aButton = (JButton) anEvent.getSource();
	
	   resultExpression = Double.toString(number1) + " + " +   
                             Double.toString(number2);
	   if (sum > 0)
	       aButton.setBackground(Color.RED);
	   else if (sum < 0)
	       aButton.setBackground(Color.GREEN);
	   resultExpression = resultExpression + " = " +                  
                             Double.toString(sum);
	   this.setTitle(resultExpression);
    }

    public void initializeWidgets()
    {
	   operand1 = new JTextField("0.0");
	   operand1.setBounds(50,50,100,20);
	   operand2 = new JTextField("0.0");
	   operand2.setBounds(200,50,100,20);
	   aButton = new JButton("Add");
	   aButton.setBounds(100,100,150,30);
	   aButton.addActionListener(this);
    }
}