import javax.swing.*;	//for the graphics displays such as windows, buttons, etc
import java.awt.*;
import java.awt.event.*; //for the ActionListener class

public class RectangleCalculator
{
	// Objects should be class-level
	private JLabel lengthL, widthL, areaL, perimeterL;
    private JTextField lengthTF, widthTF, areaTF, perimeterTF;
    private JButton calculateB, exitB;
    CalculateButtonHandler cbHandler;
    ExitButtonHandler ebHandler;

	public void driver()
	{
	  // Create the window
	  JFrame rect = new JFrame("Rectangle Area & Perimeter");
	  rect.setSize(400, 300);
	  rect.setDefaultCloseOperation(rect.EXIT_ON_CLOSE);

	  // Get the content pane (an object of type Container)
	  Container cp = rect.getContentPane();
	  cp.setLayout( new GridLayout(5, 2) );

	  lengthL = new JLabel("Enter the length: ", SwingConstants.RIGHT);
	  widthL = new JLabel("Enter the width: ", SwingConstants.RIGHT);
	  areaL = new JLabel("The area is: ", SwingConstants.RIGHT);
	  perimeterL = new JLabel("Perimeter: ", SwingConstants.RIGHT);

	  lengthTF = new JTextField(10);
	  widthTF = new JTextField(10);
	  areaTF = new JTextField(10);
	  perimeterTF = new JTextField(10);

	  areaTF.setEditable(false);
	  perimeterTF.setEditable(false);

	  calculateB = new JButton("Calculate");
	  exitB = new JButton("Exit");

	  // Add our components to the content pane container
	  cp.add(lengthL);
	  cp.add(lengthTF);
	  cp.add(widthL);
	  cp.add(widthTF);
	  cp.add(areaL);
	  cp.add(areaTF);
	  cp.add(perimeterL);
	  cp.add(perimeterTF);
	  cp.add(calculateB);
	  cp.add(exitB);


	  rect.setVisible(true);

	  // Instantiate listeners
	  cbHandler = new CalculateButtonHandler();
	  ebHandler = new ExitButtonHandler();

	  // Register the listeners with their respective components
	  calculateB.addActionListener(cbHandler);
	  exitB.addActionListener(ebHandler);

	}


	// In order to run our program, we need to instantiate this class
	// and then invoke the driver() method
	public static void main(String[] args)
	{
		RectangleCalculator r = new RectangleCalculator();
		r.driver();
	}


	//This class implements the ActionListener interface
	//It is created to create a listener (aka "handler") for our calculateB button
	private class CalculateButtonHandler
	  implements ActionListener
	{
	  // Implementing an interface rquires writing a body for ALL of the methods in that interface.
	  // In the case of ActionListener, there is only one method, so that is all we have to implement.
	  // The actionPerformed() method will be automatically invoked whenever an event is generated
	  // by the component.  (Of course, we have to remember to first register the listener with the component).
	  public void actionPerformed(ActionEvent e)
	  {
		double width, length, area, perimeter;
		length = Double.parseDouble(lengthTF.getText() );
		width = Double.parseDouble(widthTF.getText() );
		area = length * width;
		perimeter = (length+width) * 2;

		areaTF.setText("" + area); // the setText() method changes the display of a text field
		perimeterTF.setText("" + perimeter);
	  } //end method actionPerformed
	} //end class CalculateButtonHandler


	//This class implements the ActionListener interface
	//It is created to create a listener (aka "handler") for our exitB button
	  private class ExitButtonHandler implements ActionListener
	  {
		public void actionPerformed(ActionEvent e)
		{
		  System.exit(0);
		} //end method actionPerformed
	  } //end class ExitButtonHandler

} //end class RectangleCalculator